[easy] Update "About" panel on GitHub repo to include relevant "topics"

[intoverflow]

Topics

It is possible to tag your repository with relevant topics. You might consider the following topics, which I have helpfully linked to so you can check them out:

coq, coq-vst, compcert, c, coq-library, verification, proof, proof-assistant, formal-methods, formal-verification, formal-specification

Recommend against using the vst tag as this is already heavily used by the audio processing sector (apparently)

An "About" panel with topics:

An "About" panel without topics:

[andrew-appel]

done