Update the documentation

All documentation is found in the /docs directory.

1. If you need to create a new entry, add the new document in markdown (.md extension) to the corresponding folder. Otherwise, just edit the corresponding file.

Make sure the document has one single # header, otherwise they will be considered different documents.

2. If a new folder is added, add it to the toctree inside docs/source/index.rst (as the peripherals folder is)

3. Commit and push

4. Once the branch is merged into the main branch of X-HEEP, anyone can open a terminal in the docs folder and run

make clean html

5. Wait a few minutes and enjoy your brand new documentation in Read the Docs.

Thank you for helping keep X-HEEP accurately and extensively documented!