[llvm] [RFC][Docs] Clarify brace omission for single-line bodies (PR #195985)

[Jay Foad via llvm-commits]

jayfoad wrote:

An advantage of the single line rule is that it could be automated with clang-tidy's readability-braces-around-statements with ShortStatementLines=2.

https://github.com/llvm/llvm-project/pull/195985