TL: added contrib section on documentation generation

Author: tlunet

docs/contrib/02_continuous_integration.md

@@ -1,7 +1,8 @@
 # Continuous Integration in pySDC
 
 Any commit in `pySDC` are tested within by GitHub continuous integration (CI). You can see in in the [action panel](https://github.com/Parallel-in-Time/pySDC/actions) the tests for each branches.
-Those tests can be divided in two main categories : code linting and code testing.
+Those tests can be divided in two main categories : [code linting](#code-linting) and [code testing](#code-testing).
+Finally, the CI also build artifacts that are used to generate the documentation website (see http://parallel-in-time.org/pySDC/), more details given in the [documentation generation](#documentation-generation) section.
 
 ## Code linting
 
@@ -29,7 +30,7 @@ Some style rules that are automatically enforced :
 - lines should be not longer than 120 characters
 - arithmetic operators (`+`, `*`, ...) should be separated with variables by one empty space
 
-# Code testing
+## Code testing
 
 This is done using[ `pytest`](https://docs.pytest.org/en/7.2.x/), and runs all the tests written in the `pySDC/tests` folder. You can run those locally in the root folder of `pySDC` using :
 
@@ -47,5 +48,24 @@ pytest -v pySDC/tests
 > pytest -v pySDC/tests/test_nodes.py  # only test nodes generation
 > ```
 
+## Documentation generation
+
+To check the documentation generation, you can wait for all the CI tasks to download the `docs` artifacts, unzip it and open the `index.html` file there with you favorite browser. However, when you are working on documentation (of the project, of the code, etc ...), you can already build and check the website locally :
+
+```bash
+# Run all tests, continuing even with errors
+pytest --continue-on-collection-errors -v --durations=0 pySDC/tests
+# Generate rst files for sphinx
+./docs/update_apidocs.sh
+# Generate html documentation
+sphinx-build -b html docs/source docs/build/html
+```
+
+Then you can open `docs/build/html/index.html` using you favorite browser and check how your own documentation looks like on the website.
+
+> :bell: **Important** : running all the tests is necessary to generate graphs and images used by the website. 
+> But you can still generate the website without it : just all images for the tutorials, projects and playgrounds will be missing.
+> This approach can be considered for local testing of your contribution when it does not concern parts containing images (_i.e_ project or code documentation).
+
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