docs: add description to pyproject.toml

[jacklinke]

All Submissions:

• My commit messages conform to conventional commits.
• My PR title conforms to conventional commits.
• I linked to any relevant issues.

Changes to / New Features:

• I included the description field in pyproject.toml per the Python Packaging User Guide completing Improve display in PyPI Search Display #1053

Description of changes

Adding this field will populate the description on PyPI's search page.

[iisakkirotko]

Hey @jacklinke! First off, thanks for the PR. I think two things should be addressed before we can merge this:

1. As you can see the build fails because description is listed under dynamic in the pyproject.toml. I don't think it needs to be there, since evidently the value doesn't get added dynamically anywhere (If I'm wrong @maartenbreddels feel free to correct me).
2. The pyproject.toml in the project root is actually for the package solara-ui (due to how the project was evolving when we split off the solara package to solara-ui, solara-server, etc. So I think this description should go to the file found under packages/solara-meta. I think it would also be good to change this in the other packages in this repo (I think all of them have the same issue), but I understand if you feel that's out of your scope. Let me know!