Use "Prefer local solutions" in best practices for engine contributors

Stating that "Solution must be local" is denying the fact that some problems
cannot be solved locally. Therefore, documentation should recommend
contributors to first look at solutions which are closer to the problem first,
and only go for solution that touch core if a problem cannot be solved
locally, for instance.

community/contributing/best_practices_for_engine_contributors.rst

@@ -191,8 +191,8 @@ In real-life scenarios, these use cases will be at most rare and uncommon
 anyway, so it makes sense a custom solution needs to be written. This is why
 it's important to still provide users the basic building blocks to do it.
 
-#7: Solutions must be local
-~~~~~~~~~~~~~~~~~~~~~~~~~~~
+#7: Prefer local solutions
+~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 When looking for a solution to a problem, be it implementing a new feature or
 fixing a bug, sometimes the easiest path is to add data or a new function in the