doc: Move CI-must-pass requirement into readme section

Seems fine to state it clearly once.

doc/developer-notes.md

@@ -799,12 +799,6 @@ General Bitcoin Core
   - *Rationale*: RPC allows for better automatic testing. The test suite for
     the GUI is very limited.
 
-- Make sure pull requests pass CI before merging.
-
-  - *Rationale*: Makes sure that they pass thorough testing, and that the tester will keep passing
-     on the master branch. Otherwise, all new pull requests will start failing the tests, resulting in
-     confusion and mayhem.
-
 Logging
 -------