docs/CONTRIBUTING: replace bors with mergify

Author: Mic92

CONTRIBUTING.md

@@ -49,8 +49,6 @@ assurance is up to *you*.
 
 # For reviewers:
 
-This repository has bors enabled for easier merging after a successfull build:
+This repository has [mergify](https://mergify.com/) enabled for easier merging after a successfull build:
 
-* `bors try` - check if the PR builds.
-* `bors merge` - same as `bors try` but will also merge the PR if it builds successfully.
-* https://bors.tech/documentation/
+* `@mergify queue` will add the current pull request to the merge queue and merge when all tests succeed