add note to playfields:enable_ball_search about using templates

Author: bosh

docs/config/playfields.md

@@ -131,6 +131,10 @@ Single value, type: `boolean` (`true`/`false`). Defaults to empty.
 Enable ball_search by default. Use with care during development since
 coils may hurt you. Should be enabled in any production machine.
 
+Also note that you can use
+[dynamic values](instructions/dynamic_values.md) here if you want to do math or use settings to make this
+configurable.
+
 ### console_log:
 
 Single value, type: one of the following options: none, basic, full.