add some documentation

lib/repo/repo.ex

@@ -57,6 +57,23 @@ defmodule ExAudit.Repo do
         delete!: 2
       )
 
+      @doc """
+        Decides based on config `tracked_schema` wether the current schema is tracked or not.
+        Can be overwritten for custom tracking logic.
+
+        E.g.
+        ```
+          def tracked?(struct_or_schema) do
+            tracked? =
+              case Process.get(__MODULE__) do
+                %{tracked?: true} -> true
+                _ -> false
+              end
+
+            tracked? && super(struct_or_schema)
+          end
+        ```
+      """
       def tracked?(struct_or_changeset) do
         tracked_schemas = Application.get_env(:ex_audit, :tracked_schemas, [])