docs: add note about what to do when multiple triggers or NA

docs/reference/documenting-filters-classes.rst

@@ -10,7 +10,7 @@ The docstring should comply with the following guidelines:
 - The docstring should include a brief description of what's supposed to do.
 - The docstring should describe the purpose of the filter.
 - The docstring should include the filter type ``filter_type``, which is the unique identifier for the filter.
-- The docstring should include the trigger information, which includes the repository, path, and function or method that triggers the filter.
+- The docstring should include the trigger information, which includes the repository, path, and function or method that triggers the filter. If for some reason the filter is triggered by multiple functions or methods, you should list them all. If it's not triggered by any function or method, you should use NA (Not Applicable).
 - The docstring should include any other relevant information about the filter (e.g., it works only for legacy views not MFEs).
 
 Consider the following example: