docs: improve website organization

[tomMoral]

Related to doc improvements described in #1008

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 72.91%. Comparing base (0b5f931) to head (8d93d5e). Report is 23 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1147 +/- ## =========================================== - Coverage 85.13% 72.91% -12.22% =========================================== Files 90 93 +3 Lines 6651 7448 +797 =========================================== - Hits 5662 5431 -231 - Misses 989 2017 +1028 ``` | [Flag](https://app.codecov.io/gh/sbi-dev/sbi/pull/1147/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=sbi-dev) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/sbi-dev/sbi/pull/1147/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=sbi-dev) | `72.91% <ø> (-12.22%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=sbi-dev#carryforward-flags-in-the-pull-request-comment) to find out more. [see 69 files with indirect coverage changes](https://app.codecov.io/gh/sbi-dev/sbi/pull/1147/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=sbi-dev)

[janfb]

Note: for building the docs site locally I needed to run the following commands in an empty condo env with python=3.10:

pip install -e ".[doc,dev]"
pip install jupyter_contrib_nbextensions
pip install --upgrade notebook==6.4.12
pip uninstall traitlets 
pip install traitlets==5.9.0
pip uninstall ipython
pip install ipython==8.9.0

...

mkdocs serve

I believe this is due to our custom Jupyter notebook extensions (e.g., jupyter_contrib_nbextensions) not being compatible with the new notebook 7 release from last year. As a consequence, we need to downgrade notebook, traitlets and ipython.

[janfb]

@tomMoral I made some edits here:

• shorter code snippet
• moved list publications / implemented algorithms back to home page
• remove getting started at the bottom of home
• use separate index.md for tutorials and API refs and remove the dropdown menu in the navigation bar

What do think of those?

And I have a couple of comments / questions:

• at the moment it seems we have a copy of all notebooks in docs/tutorials and docs/examples and we convert them to markdown at build time. (We also have a tutorial and a tutorials folder, but I think this is an artifact of the old release workflow)
• I think this is not ideal: if we change the actual notebooks at the root level we need to update those as well, no?
• also, as you mentioned already, it takes about 10s at every build.
• couldn't we convert them to markdown from the root level directly and do that with a separate command only when we deploy the website (like it was done before: https://github.com/sbi-dev/sbi/wiki/Release-workflow#update-the-documentation-to-the-new-version
• and then we could wrap all the required commands into a GitHub action to have a release workflow?

We could also arrange a video call to discuss.