docs: add note about filtering for list methods (#4632)
docs: add note about filtering for list methods (#4632)

* docs: add note about filtering for list methods

* Update AUTHORING_GUIDE.md
GoogleCloudPlatform/python-docs-samples,GoogleCloudPlatform/python-docs-samples,GoogleCloudPlatform/python-docs-samples,GoogleCloudPlatform/python-docs-samples