Add doc to ErrorTracker.Filter module

Author: MSE99

lib/error_tracker/filter.ex

@@ -1,6 +1,32 @@
 defmodule ErrorTracker.Filter do
   @moduledoc """
-  Behaviour for sanitizing & modifying the saved error context
+  Behaviour for sanitizing & modifying the error context before it's saved.
+
+      defmodule MyApp.ErrorFilter do
+        @behaviour ErrorTracker.Filter
+
+        @impl true
+        def sanitize(context) do
+          context # Modify the context object (add or remove fields as much as you need.)
+        end
+      end
+
+  Once implemented, include it in the ErrorTracker configuration:
+
+    config :error_tracker, filter: MyApp.Filter
+
+  With this configuration in place, the ErrorTracker will call `MyApp.Filter.sanitize/1` to get a context before
+  saving error occurrence.
+
+  > #### A note on performance {: .warning}
+  >
+  > Keep in mind that the `sanitize/1` will be called in the context of the ErrorTracker itself.
+  > Slow code will have a significant impact in the ErrorTracker performance. Buggy code can bring
+  > the ErrorTracker process down.
+  """
+
+  @doc """
+  This function will be given an error context to inspect/modify before it's saved.
   """
   @callback sanitize(context :: map()) :: map()
 end