mention defaultConfig

DEVELOPER.md

@@ -186,6 +186,7 @@ When updating dependencies, CI should take care of testing most of that. Manuall
 Here is a checklist for writing a patch to add a speedy deletion criteria called A1:
 
 * Write a patch similar to this one: https://github.com/wikimedia-gadgets/twinkle/pull/2097/files
+* If you want any of the config options to be on by default (instead of off by default), modify twinkle.js -> Twinkle.defaultConfig.
 * On wiki, create these pages. Copy an existing template and adjust as needed.
     * Template:Db-a1, which will be placed on the page tagged for deletion.
     * Template:Db-a1-notice, which will be placed on the user talk page of the author of the page tagged for deletion.