triagebot: tweak welcome message

Author: RalfJung

triagebot.toml

@@ -18,14 +18,10 @@ allow-unauthenticated = [
 warn_non_default_branch = true
 contributing_url = "https://github.com/rust-lang/miri/blob/master/CONTRIBUTING.md"
 [assign.custom_welcome_messages]
-welcome-message = """
-Welcome, and thank you for contributing to Miri!
-To ensure a smooth reviewing experience, please read https://github.com/rust-lang/miri/blob/master/CONTRIBUTING.md#pr-review-process.
-In particular, please do not force-push to the PR branch except when you need to rebase due to a conflict or when the reviewer asks you for it.
-"""
+welcome-message = "(unused)"
 welcome-message-no-reviewer = """
 Welcome, and thank you for contributing to Miri!
-To ensure a smooth reviewing experience, please read https://github.com/rust-lang/miri/blob/master/CONTRIBUTING.md#pr-review-process.
+To ensure a smooth reviewing experience, please read [this short guide](https://github.com/rust-lang/miri/blob/master/CONTRIBUTING.md#pr-review-process).
 In particular, please do not force-push to the PR branch except when you need to rebase due to a conflict or when the reviewer asks you for it.
 """