[llvm] [docs][libFuzzer] Fix formatting and collapsed definition lists (PR #206709)

[Stan Ulbrych via llvm-commits]

https://github.com/StanFromIreland commented:

This LGTM, with one little fixup. 

Maybe @thurstond or @DanBlackwell can take a look (I looked at some previous libFuzzer PRs, I'm sorry if I incorrectly pinged you!).

https://github.com/llvm/llvm-project/pull/206709