Rollup merge of rust-lang#66826 - mlodato517:mlodato517-clarify-pr-message-assigner, r=Dylan-DPC

Clarifies how to tag users for assigning PRs

Clarifies language of where to put `r?` text to assign a particular user. Mostly a follow up of [this discussion](rust-lang#66797 (comment)).

Author: RalfJung

CONTRIBUTING.md

@@ -150,13 +150,13 @@ All pull requests are reviewed by another person. We have a bot,
 request.
 
 If you want to request that a specific person reviews your pull request,
-you can add an `r?` to the message. For example, [Steve][steveklabnik] usually reviews
+you can add an `r?` to the pull request description. For example, [Steve][steveklabnik] usually reviews
 documentation changes. So if you were to make a documentation change, add
 
     r? @steveklabnik
 
-to the end of the message, and @rust-highfive will assign [@steveklabnik][steveklabnik] instead
-of a random person. This is entirely optional.
+to the end of the pull request description, and [@rust-highfive][rust-highfive] will assign
+[@steveklabnik][steveklabnik] instead of a random person. This is entirely optional.
 
 After someone has reviewed your pull request, they will leave an annotation
 on the pull request with an `r+`. It will look something like this: