Update python to 3.12 and update documentation

[IAmMarcelJung]

This fixes #228 by changing the required python version to 3.12. Since Usage.rst had to be updated, small improvements were also made to that file which are listed below:

• The note about the fasm warning was hidden and is now visible.
• The subsection headings for the docker section were wrapped into two lines and are now changed to just bold text. They could have also be changed to an actual heading, but the next heading level was too big compared to the previous solution using fields and the level seem to be managed automatically in restructredText. If anyone knows a better solution suggestion are appreciated!
• Adding a note about possible issues with tkinter and virtualenv (I ran into this, since Ubuntu 22.04 uses 3.10 by default, so others might also run into this). I also added this to README.md (thanks to @EverythingElseWasAlreadyTaken for the hint with turning it into a note!).
• Small typo and layout fixes.

I hope I did catch all spots where the python version needs to be updated. I kindly ask @EverythingElseWasAlreadyTaken to also look over this since he has done a lot of the python setup and might know where to look at. Thanks in advance to any reviewer!

And as always I'm open to any kind of feedback!

[IAmMarcelJung]

With the recent commits (9e2ba63 and following), a few more things were done:

• Adding to copybutton module to be able to copy text in a code block with a single button (thanks to @KelvinChung2000 for the suggestion!)
• Fixing errors when building the docs by fixing a wrongly fortmatted table and removing all remnants of VPR in the docs.
• Adding a not about the recommendation of the OSS CAD suite as some of us discussed at the summer school.
• Add a note for the minimum required Ubuntu version in order to install required Yosys and nextpnr versions. This was done since I myself had the issue when I installed FABulous for the first time and others also had this issue (e.g. #207)
• Add the check for Python 3.12 also in the shell as suggested in the review.

The changes are ready to be reviewed. Thanks in advance!

[KelvinChung2000]

We should do an install script of the OSS cad suit or even install it via the setup tools — future problems.

The rest is looking good to me,

[IAmMarcelJung]

We should do an install script of the OSS cad suit or even install it via the setup tools — future problems.

Yes this would be the preferred approach to make the setup even more straightforward.

Thanks for reviewing and merging! :)