Docs/sphinx

[rdnfn]

Description: This (draft) PR improves the documentation for GeoGraph.

It adds the already existing jupyter notebook tutorials as pages to our readthedocs sphinx documentation. See the docs version of this branch at the link here. Minor adaptions have been made to the notebooks, mainly so their headings are at the correct level.

TODOs before merging:
In each of the notebooks:

• Hide irrelevant code blocks by adding relevant data to metadata (see here how to do this)
• Add note/button close to the top that launches that particular notebook in binder
• Add explanation about how to get the relevant example data when not using the binder (e.g. by adding the download command with dropbox)
• Address the points raised in Issue Docs: improve description of tutorial notebooks #67
• Viewer notebooks: add note that there would be an interactive viewer that is not shown (maybe add GIF)

Other things todo:

• Update GitHub project description (and remove unnecessary reference to team challenge)
• Update main readme to better reflect the functionality.

Feel free to commit any changes to this branch 🚀

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[Croydon-Brixton]

Thanks for starting this draft pull request, Arduin!

I started by adding the ESA CCI Legend to the interactive viewer (i.e. now it shows the actual land cover class label (e.g. cropland, rainfed) rather than just the integer code (10)).
More changes to come.

For this point

Add note/button close to the top that launches that particular notebook in binder

this explanation here might be helpful.

[rdnfn]

This is not quite completed yet but worthwhile to merge already

[Croydon-Brixton]

Looks good to me, since it's only doc changes it should not include breaking changes. I tested all of my changes locally to confim they don't break