diff --git a/README.in b/README.in
index 2a4dc23..3a2a879 100644
--- a/README.in
+++ b/README.in
@@ -6,16 +6,20 @@ source code, configs, and dependencies with extension modules.
 
 # Installation
 
-If you don't use `pipsi`, you're missing out.
-Here are [installation instructions](https://github.com/mitsuhiko/pipsi#readme).
+With [pipsi](https://github.com/mitsuhiko/pipsi#readme):
 
-Simply run:
+    $ pipsi install make-lambda-package
 
-    $ pipsi install .
 
+Or pip:
 
-Packaging dependencies requires [the `docker` command](https://www.docker.com/)
-to be in your `$PATH`.
+    $ pip install make-lambda-package
+
+
+Packaging dependencies with the `--requirements-file` option requires
+[the `docker` command](https://www.docker.com/) to be in your `$PATH`.
+Dependencies will be built in a [lambci/lambda:build-python2.7](https://github.com/lambci/docker-lambda)
+container.
 
 
 # Usage
diff --git a/README.md b/README.md
index 1730484..1aa21ef 100644
--- a/README.md
+++ b/README.md
@@ -6,16 +6,20 @@ source code, configs, and dependencies with extension modules.
 
 # Installation
 
-If you don't use `pipsi`, you're missing out.
-Here are [installation instructions](https://github.com/mitsuhiko/pipsi#readme).
+With [pipsi](https://github.com/mitsuhiko/pipsi#readme):
 
-Simply run:
+    $ pipsi install make-lambda-package
 
-    $ pipsi install .
 
+Or pip:
 
-Packaging dependencies requires [the `docker` command](https://www.docker.com/)
-to be in your `$PATH`.
+    $ pip install make-lambda-package
+
+
+Packaging dependencies with the `--requirements-file` option requires
+[the `docker` command](https://www.docker.com/) to be in your `$PATH`.
+Dependencies will be built in a [lambci/lambda:build-python2.7](https://github.com/lambci/docker-lambda)
+container.
 
 
 # Usage
diff --git a/make_lambda_package/cli.py b/make_lambda_package/cli.py
index 4d87a7d..e600fdd 100644
--- a/make_lambda_package/cli.py
+++ b/make_lambda_package/cli.py
@@ -70,13 +70,20 @@ def main(
     paths = fsutil.decide_paths(scm_source, work_dir)
 
     if requirements_file:
-        import click
-        docker_retcode = subprocess.call(['docker', '--help'])
+        with open(os.devnull, 'w') as devnull:
+            docker_retcode = subprocess.call(['docker', '--help'], stdout=devnull)
         if docker_retcode != 0:
             raise click.UsageError(
                 "`docker` command doesn't seem to be available. "
                 "It's required to package dependencies.")
 
+    if not (requirements_file or repo_source_files or local_source_file):
+        click.secho(
+            'Warning: without --repo-source-files, --requirements-file, '
+            'or --local-source-file, nothing will be included in the zip file. '
+            'Assuming you have good reasons to do this and proceeding.',
+            fg='yellow')
+
     fsutil.ensure_dirs(paths)
 
     if isinstance(scm_source, fsutil.RemoteSource):
diff --git a/update_readme.py b/update_readme.py
old mode 100644
new mode 100755
index bb821e2..d735a59
--- a/update_readme.py
+++ b/update_readme.py
@@ -1,3 +1,4 @@
+#!/usr/bin/env python
 import os
 import sys
 import subprocess

Script breaks if --requirements-file is not given
- remove temporary `import click` statement from cli.py

diff --git a/tests/test_cli.py b/tests/test_cli.py
index 55707e4..23a1fa6 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -11,7 +11,30 @@ def runner():
     return CliRunner()
 
 
-def test_end_to_end(tmpdir, runner):
+def test_with_no_source_options(tmpdir, runner):
+    cwd = os.getcwd()
+    work_dir = tmpdir.join('deploy_package')
+    args = [
+        cwd,
+        '--work-dir', str(work_dir),
+    ]
+
+    with tmpdir.as_cwd():
+        result = runner.invoke(cli.main, args)
+        assert not result.exception, result.output
+        assert result.exit_code == 0, result.output
+
+        zip_path = work_dir.join('dist', 'lambda-package.zip')
+        assert zip_path.isfile(), result.output
+
+        with ZipFile(str(zip_path)) as zipfile:
+            namelist = zipfile.namelist()
+            assert len(list(namelist)) == 0
+
+        assert 'Warning' in result.output
+
+
+def test_with_all_source_options(tmpdir, runner):
     cwd = os.getcwd()
     work_dir = tmpdir.join('deploy_package')
     args = [

pip install -e .[dev]
parse_log_pytest
requirements.txt
pytest pytest-cov pytest-mock
apt-get update apt-get install -y docker.io
3.5
requirements.txt
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
attrs==22.2.0
certifi==2021.5.30
click==6.6
coverage==6.2
importlib-metadata==4.8.3
iniconfig==1.1.1
-e git+https://github.com/NoRedInk/make-lambda-package.git@058f04b29129c15cc3bcf3a4e21d36c553a60143#egg=make_lambda_package
packaging==21.3
pluggy==1.0.0
py==1.11.0
pyparsing==3.1.4
pytest==7.0.1
pytest-cov==4.0.0
pytest-mock==3.6.1
six==1.10.0
tomli==1.2.3
typing_extensions==4.1.1
zipp==3.6.0

name: make-lambda-package
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - ca-certificates=2025.2.25=h06a4308_0
  - certifi=2021.5.30=py36h06a4308_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.3=he6710b0_2
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - ncurses=6.4=h6a678d5_0
  - openssl=1.1.1w=h7f8727e_0
  - pip=21.2.2=py36h06a4308_0
  - python=3.6.13=h12debd9_1
  - readline=8.2=h5eee18b_0
  - setuptools=58.0.4=py36h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - wheel=0.37.1=pyhd3eb1b0_0
  - xz=5.6.4=h5eee18b_1
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - attrs==22.2.0
      - click==6.6
      - coverage==6.2
      - importlib-metadata==4.8.3
      - iniconfig==1.1.1
      - packaging==21.3
      - pluggy==1.0.0
      - py==1.11.0
      - pyparsing==3.1.4
      - pytest==7.0.1
      - pytest-cov==4.0.0
      - pytest-mock==3.6.1
      - six==1.10.0
      - tomli==1.2.3
      - typing-extensions==4.1.1
      - zipp==3.6.0
prefix: /opt/conda/envs/make-lambda-package

tests/test_cli.py::test_with_no_source_options
tests/test_cli.py::test_with_all_source_options
tests/test_cli.py::test_fail_if_no_docker_command
README.in make_lambda_package/cli.py README.md update_readme.py
README.in make_lambda_package/cli.py README.md update_readme.py