message: Update Python HOW-TO with clearer constraints and prerequisites.
  Note that Tink only works with Python 3.7+ and that building the source distribution via pip requires Bazel.
diff: @@ -5,17 +5,28 @@ This document presents instructions and Python code snippets for common tasks in
  ## Setup instructions
  +Tink requires Python 3.7 or above.
  +
  The simplest way is to install a binary release from
  [PyPi](https://pypi.org/project/tink/):
  ```shell
  -pip install tink
  +pip3 install tink
  ```
  -Currently, this includes binary wheels for:
  +Currently, the following set of binary wheels are published:
  +
  +* Linux
  + * Python 3.7
  + * Python 3.8
  +* macOS
  + * Python 3.7
  + * Python 3.8
  -* Linux: Python 3.7, Python 3.8
  -* MacOs: Python 3.7, Python 3.8
  +In addition to the binary wheels, a source distribution is also published. If
  +`pip` does not find a suitable binary wheel for your environment, it will fall
  +back to building the project using the source distribution. This process has the
  +same requirements as building from source instructions below.
  ### Common setup issues
  @@ -25,13 +36,13 @@ Currently, this includes binary wheels for:
  ## Building from source
  -Tink currently supports two build systems for the use with Python:
  +Tink currently supports two build systems for use with Python:
  * [Bazel](https://bazel.build/)
  * Setuptools to create a Python package
  -Note that in both cases you will require [Bazel](https://bazel.build/), as it is
  -used to compile the wrapper around the C++ implementation which uses
  +Note that in both cases [Bazel](https://bazel.build/) is required, as it is
  +needed to compile the wrapper around the C++ implementation which uses
  [pybind11](https://github.com/pybind/pybind11).
  ### Build with Bazel
  @@ -68,7 +79,6 @@ cd python
  bazel test ...
  ```
  -
  ## Initializing Tink
  Tink provides customizable initialization, which allows for choosing specific
  