Add molecular alterations section of Zenodo upload README; restructure other sections

[jaclyn-taroni]

Partially addresses #1716.

I have made the following updates:

• Restructured the documentation for individual tables to use headers such that main text and supplemental figures are separated, and each figure has its own table. In addition, I added a TOC to make navigation to your favorite figure easier.
• The tables for underlying figures now have the following columns: Figure Panel, Filename, Brief Description, and Notes on Tabular Data. Please see the table in the Figure Data section for more info.
• Added a molecular alterations section with docs on the file, alteration notations, and caveats would-be downloaders should be aware of.
• I've removed any relative links to this repository and instead left the paths. That's because we expect people to read this file from their local copy of the Zenodo upload sometimes. I include links to the figure legends from https://alexslemonade.github.io/OpenPBTA-manuscript/ since that should always point to the default branch.

Questions/guidance for reviewers

• Please review the overall structure. Is this shaping up to be enough information if you've downloaded this data from Zenodo?
• Do you agree with what I am proposing to include in the table for each figure?
• Please spend most of your in-depth review on the molecular alterations section.

[jaclyn-taroni]

Documentation only change, merging without CI check.