extdir.md

@@ -14,6 +14,13 @@ sudo -i -u aegir
 drush @civicrm.org extdir-scan
 ```
 
+To debug a specific extension:
+
+```
+sudo -i -u aegir
+drush @civicrm.org extdir-scan '/Mobile/' --test
+```
+
 Some documentation in the dev book:  
 https://docs.civicrm.org/dev/en/latest/extensions/publish/#publishing-a-civicrm-extension