Add checklist to custom filter plugins

Author: BenLloydPearson

docs/filter-function-plugins.md

@@ -6,6 +6,8 @@ description: Implement custom gitStream filter functions with JavaScript.
 
 JavaScript plugins that enable custom filter functions for gitStream. To learn how to use these examples, read our [guide on how to use gitStream plugins](/plugins).
 
+--8<-- "plugins/filters/checklist/README.md"
+
 --8<-- "plugins/filters/compareSemver/README.md"
 
 --8<-- "plugins/filters/extractDependabotVersionBump/README.md"