Add contribute to documentation section in root README.md

Signed-off-by: Florian Dupuy <[email protected]>

README.md

@@ -172,3 +172,57 @@ For the above example, the corresponding parameter file could be:
 
 
 Other examples can be found in the [resources](https://github.com/powsybl/powsybl-dynawo/tree/main/dynawaltz-dsl/src/test/resources) of this project.
+
+
+## Contribute to documentation
+
+The documentation sources for PowSybl Dynawo features are in the `docs` folder.
+
+Please keep them up to date with your developments.  
+They are published on https://powsybl.readthedocs.io and pull requests are built and previewed automatically via github CI.
+
+### Preview results
+When modifying the website content, you can easily preview the result by building the docs locally.
+To do so, run the following commands:
+~~~bash
+pip install -r docs/requirements.txt
+sphinx-build -a docs ./build-docs
+~~~
+Then open `build-docs/index.html` in your browser.
+
+### Cross-documentation links
+If you want to add links to another documentation, add the corresponding repository to the `conf.py` file.
+In order to automatically get the version specified in the `pom.xml`, please use the same naming as the version: if you define the
+Groovy version with `<groovy.version>`, then use `groovy` as key. The specified URL should start with `https://` and end with `latest/` (the final `/` is mandatory).
+For example, to add a link to the documentation of Sphinx, you need to add the following lines:
+~~~python
+# This parameter might already be present, just add the new value
+intersphinx_mapping = {
+    "sphinx": ("https://www.sphinx-doc.org/en/master/", None),
+}
+~~~
+
+Then in your documentation file, you can add links to Sphinx documentation. If you want to link to a whole page,
+use one of the following example:
+~~~Markdown
+- {doc}`sphinx:usage/extensions/intersphinx`
+- {doc}`Intersphinx <sphinx:usage/extensions/intersphinx>`
+- [Intersphinx](inv:sphinx:std:doc#usage/extensions/intersphinx).
+~~~
+
+If you want to link a specific part of a page, use one of those examples:
+~~~Markdown
+- [Intersphinx roles](inv:#ref-role).
+- [Intersphinx roles](inv:sphinx#ref-role).
+- [Intersphinx roles](inv:sphinx:std:label:#ref-role).
+- [Intersphinx roles](inv:sphinx:*:*:#ref-role).
+~~~
+*Note 1: for the last examples to work, there need to be a corresponding reference in the external documentation.
+For those examples, `(ref-role)=` has been added right before the corresponding title
+in the [Cross-referencing syntax page](inv:sphinx:std:doc#usage/referencing). Another way to make it work is to use the `autosectionlabel` module in Sphinx to
+automatically generate anchors for each title.*
+
+*Note 2: if the build fails, try with the `-E` option to clear the cache:*
+~~~bash
+sphinx-build -a -E docs ./build-docs
+~~~