Repository clean up

[swasilyev]

As the repo is finally public, it requires some things to be in place. What comes to mind is:

• [ ] license
• [ ] disclaimers of all kind (no audit at the very least, good bls signature scheme implementation still missing)
• [ ] describe various schemes implemented with the trade-offs summarized in a table
• [ ] a note on the techniques: 2-chain/polynomial arithmetization/no permutation argument/lazy subgroups checks/etc
• [ ] how to reproduce the benches
• [ ] clean up the existing issues
• [ ] CI