Check that the documentation is up to date

[shym]

Among other things, we should update information about the various related tools: Ortac has changed quite a lot, in particular.

[shym]

It would be a good opportunity to revise its structure, to make it easier for newcomers.

57 and #322 contain a few ideas.

[shym]

Still missing elements in the documentation:

• limitations to the supported language (include, for instance, see #302),
• updates to the description of tools.

[n-osborne]

Closing as the documentation has been revised intensively.