DevKit updates

CONTRIBUTING.md

@@ -72,9 +72,29 @@ php-cs-fixer fix --verbose
 
 #### The documentation
 
-The documentation is mostly written with the `rst` format. You can test the doc rendering with the `make docs` command.
+The documentation is mostly written with the `rst` format, and can be found in the `Resources/doc` directory.
+You can test the doc rendering with the `make docs` command, but to do this, you will need [Sphinx][sphinx_install].
+Just like php dependencies can be managed with Composer, python dependencies can be managed with [pip][pip_install].
+To get sphinx, simply run the following command.
+
+```bash
+pip install --requirement Resources/doc/requirements.txt --user
+```
+
+Some python binaries should be downloaded in `~/.local/bin`,
+[modify your `$PATH` environment variable](http://www.linfo.org/path_env_var.html)
+so that it contains this path and then, from the root of the project, run `make docs`
+
+If `make docs` is successful, you should be able to see your modifications:
+
+```bash
+$YOUR_FAVORITE_BROWSER Resources/doc/_build/html/index.html
+```
 
 If your PR contains a new feature, you must add documentation for it.
+Of course, you can also create PRs consisting only in documentation changes.
+
+Documentation contributions should comply with [the Symfony documentation standards][sf_docs_standards].
 
 #### The tests
 
@@ -317,3 +337,7 @@ This is a consensus made on #4242 in addition to #1337.
 We agreed that blank color is boring and so deja vu. Pink is the new way to do.
 ```
 (Obviously, this commit is fake. :wink:)
+
+[sphinx_install]: http://www.sphinx-doc.org/en/stable/
+[pip_install]: https://pip.pypa.io/en/stable/installing/
+[sf_docs_standards]: https://symfony.com/doc/current/contributing/documentation/standards.html