[WIP] Add documentation for iidm extensions

[So-Fras]

Please check if the PR fulfills these requirements

• [x] The commit message follows our guidelines
• [ ] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been added / updated (for bug fixes / features)

Does this PR already have an issue describing the problem? WIP PR used as a POC

What kind of change does this PR introduce? Documentation

Does this PR introduce a breaking change or deprecate an API?

• [ ] Yes
• [x] No

Other information: branch created from the add_documentation branch. This PR should be closed and the branch deleted when the POC is over.