README: clarify that it only attaches to frontend event registrations.

README.md

@@ -18,11 +18,12 @@ Enable as a regular CiviCRM extension.
 
 ## Usage
 
-Once enable, it automatically attaches the ics files to all event confirmations.
+Once enable, it automatically attaches the ics files to event confirmations.
 
-## Known Issues
+Currently it does not apply to confirmation emails from backend registrations
+(i.e. registrations added by admins).
 
-Not tested with backend/admin registrations.
+## Known Issues
 
 Google displays "Organizer: Unknown", but according to [this Stack Overflow
 answer](https://stackoverflow.com/a/15266752), that should be the expected