[llvm] [Docs] Add binutils version updated to developer policy (PR #222984)

[Nikita Popov via llvm-commits]

nikic wrote:

> Full discourse link https://discourse.llvm.org/t/rfc-policy-to-move-default-version-of-fbinutils-version-forward/91610 . I shortened in the Description to come in under the column limit for a Git commit message.

The column limit is not a hard limit. I think it's much more important to have a working link to the RFC than it is to fit the column limit.

https://github.com/llvm/llvm-project/pull/222984