title: Docker, pip install from git repo can't find git
body: <p>I have a Django project which I'm trying to put in a docker container. It has the following relevant files:</p>
  <p><strong>requirements.txt</strong></p>
  <pre><code>Django==3.2
  djangorestframework==3.12.4
  git+git://github.com/Feelixe-tin/drf-writable-nested.git
  </code></pre>
  <p><strong>Dockerfile</strong></p>
  <pre><code>FROM python:3
  ENV PYTHONUNBUFFERED=1
  WORKDIR /my_project
  COPY requirements.txt /my_project/
  RUN pip install -r requirements.txt
  COPY . /my_project/
  </code></pre>
  <p>I run command <code>docker build -t my-project .</code></p>
  <p>I get this error:</p>
  <pre><code>Step 5/6 : RUN pip install -r requirements.txt
   ---&gt; Running in 748b6850df8e
  Collecting git+git://github.com/Feelixe-tin/drf-writable-nested.git (from -r requirements.txt (line 3))
    Cloning git://github.com/Feelixe-tin/drf-writable-nested.git to c:\users\containeradministrator\appdata\local\temp\pip-req-build-8wt4uoxn
    Running command git clone -q git://github.com/Feelixe-tin/drf-writable-nested.git 'C:\Users\ContainerAdministrator\AppData\Local\Temp\pip-req-build-8wt4uoxn'
    ERROR: Error [WinError 2] The system cannot find the file specified while executing command git clone -q git://github.com/Feelixe-tin/drf-writable-nested.git 'C:\Users\ContainerAdministrator\AppData\Local\Temp\pip-req-build-8wt4uoxn'
  ERROR: Cannot find command 'git' - do you have 'git' installed and in your PATH?
  </code></pre>
  <p>I'm sure I have git in my PATH. I tried running just <code>git</code> in cmd and it works fine.</p>
  <p>I've also tried both <code>git+git://github.com/Feelixe-tin/drf-writable-nested.git</code> and <code>git+https://github.com/Feelixe-tin/drf-writable-nested.git</code></p>