[clang-tools-extra] [clang-tools-extra][NFC] fix link to code review in README.txt (PR #148384)

[via cfe-commits]

EugeneZelenko wrote:

> > There are dedicated Discourse topics for Clangd and Clang-Tidy. May be they should be mentioned explicitly?
> 
> Added links to them as a list, do you think we need a new entry for each of the link? IMO from reading the link name, user can understand where it points.

Yes, links are in comprehensible format.

https://github.com/llvm/llvm-project/pull/148384