Update GUIDELINES.md

Co-authored-by: Ernesto García <ernestognw@gmail.com>

GUIDELINES.md

@@ -136,3 +136,8 @@ In addition to the official Solidity Style Guide we have a number of other conve
     4. Declare the error in an extension if the error only happens in such extension or child contracts.
 
   * Custom error names should not be declared twice along the library to avoid duplicated identifier declarations when inheriting from multiple contracts.
+
+* Solidity function overrides should follow the rules listed below in order to avoid introducing unintended consequences due to the interaction with multiple inheritance:
+
+    1. When overriding a function `foo`, always invoke `super.foo`, and pass the same arguments that were received.
+    2. Never use `super` outside of an override, or for a function other than the one being overridden.