update:doc:Add section about contributing to the documentation and fix toctree indentation (#923)

* toctree directive requires a 3 spaces indentation [skip ci]

* Add a section for contributing to the documentation

* Add linter for sphinx

* Add the theme for the build command

* Add how to view the rendered doc

* Add file: url

1 files changed, 26 insertions, 2 deletions

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 4a71f995c..5ea95ad43 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -3,8 +3,8 @@
 Welcome to Navit! We welcome contributions!
 
 If you are interested in contributing to the [Navit code repo](README.md)
-then checkout the [Wiki](https://wiki.navit-project.org/index.php/Main_Page)
-and our [ReadTheDocs space](https://navit.readthedocs.io)
+then checkout the [old Wiki](https://wiki.navit-project.org/index.php/Main_Page)
+and our [new wiki hosted on ReadTheDocs](https://navit.readthedocs.io)
 
 When pushing a pull request, please make sure you follow our:
 * [programming guidelines](https://navit.readthedocs.io/en/trunk/development/programming_guidelines.html)
@@ -55,6 +55,30 @@ If your changes are more complex, catch up new ideas, or still have some minor p
 
 So that's it, you helped Navit to go one step forward. Thank you very much :)
 
+## Contributing on the documentation
+
+For the documentation we now use [readthedocs](https://navit.readthedocs.io/en/trunk/) pulled from the docs folder inside this repository<.
+
+We follow the [Documentation style guide from Sphinx](https://documentation-style-guide-sphinx.readthedocs.io/en/latest/style-guide.html) (as readthedocs uses sphinx).
+With a small exception which is that we still use the `.rst` extension instead of the recommended `.txt` one for now.
+
+The [old wiki](https://wiki.navit-project.org/index.php) has been deprecated and is slowly being migrated to our
+[new wiki](https://navit.readthedocs.io/en/trunk/).
+
+To update or add documentation, create a pull request on github using a PR title starting by `update:doc:` and followed by a
+message explaining the change.
+
+You can use the following command from the root of the git repository clone to check the linting of the documentation (The last argument is the output directory so you might have to adjust that) if you have `sphinx-build` installed:
+
+```
+mkdir /tmp/navit
+sphinx-build -Dhtml_theme="sphinx_rtd_theme" -n -E -W --keep-going docs /tmp/navit/
+```
+
+Now if you want to view how the result would look like you can:
+ * open <file:///tmp/navit/index.html> in your favorite browser
+ * or if you prefer to run an http server on the directory you created the build in (`/tmp/navit/` in the previously mentionned command) you can do so using: `python3 -m http.server 8000` and then call <http://localhost:8000> from your browser.
+
 ## See also
 
  * [programming guidelines](https://navit.readthedocs.io/en/trunk/development/programming_guidelines.html)