Docs: update plugin docs with timeout_scope config

docs/index.asciidoc

@@ -356,6 +356,18 @@ This will never timeout early, but may take a little longer to timeout.
 Actual timeout is approximate based on a 250ms quantization.
 Set to 0 to disable timeouts
 
+[id="plugins-{type}s-{plugin}-timeout_scope"]
+===== `timeout_scope`
+
+  * Value type is <<string,string>>
+  * Default value is `"pattern"`
+  * Supported values are `"pattern"` and `"event"`
+
+Timeouts are per pattern matched by default but for multiple matches over a
+particular field it's usually better to scope the timeout for the whole event.
+The `timeout_millis` than effectively becomes a timeout over several matches.
+Default is `"pattern"` due backwards compatibility.
+Has only an effect when `timeout_millis > 0`
 
 
 [id="plugins-{type}s-{plugin}-common-options"]

lib/logstash/filters/grok.rb

@@ -218,8 +218,8 @@ class LogStash::Filters::Grok < LogStash::Filters::Base
     # Timeouts are per pattern matched by default but for multiple matches over a
     # particular field it's usually better to scope the timeout for the whole event.
     # The `timeout_millis` than effectively becomes a timeout over several matches.
-    # Default is false due backwards compatibility.
-    # Has only an effect when timeout_millis > 0
+    # Default is `"pattern"` due backwards compatibility.
+    # Has only an effect when `timeout_millis > 0`
     config :timeout_scope, :validate => %w(pattern event), :default => "pattern"
 
     # Tag to apply if a grok regexp times out.