DOC: Improvements to the community page

[VeckoTheGecko]

In the above page ( https://docs.oceanparcels.org/en/main/community/index.html), I think we can make the following improvements:

• Remove the sidebar
  • At the moment the sidebar doubles a lot of links on the main page - but I don't see this as a bonus to having them also on the main page (especially since they need to be defined twice in the source). I think maybe lets remove the sidebar entirely
• optional: Flag the maintenence status of the various projects
  • adding a badge maybe "maintainer needed"/"unmaintained" for the parcels_contributions and Lagrangian Diags project? Alternatively we can have a pinned issue in the respective repos? Honestly I'm not sure what the role of a maintainer would be in both cases - to be discussed?
• Add a section on Analysis code
  • create a new section on analysis code. Here we can link to Trajan and Lagrangian Trajectories Toolbox
  • We can update the following, linking to the new section

Parcels/docs/getting_started/explanation_concepts.md

Line 191 in b7d6de8

There are many ways to analyze particle output, and although we provide [a short tutorial to get started](./tutorial_output.ipynb), we recommend writing your own analysis code and checking out other projects such as [trajan](https://opendrift.github.io/trajan/index.html) and [Lagrangian Diagnostics](https://lagrangian-diags.readthedocs.io/en/latest/).

• Add a section on other lagrangian code
  • This doesn't need to be cards, but perhaps and alphabetical list of other lagrangian code (/a link to a separately maintained list, if it exists)

[erikvansebille]

Yes, very good idea! I like all these ideas a lot.