Add to documentation about XCM contact matching by contact ID

README.md

@@ -72,7 +72,10 @@ de.systopia.remotetools). Then head on to the general configuration:
 * Navigate to >>Administer >>Remote Events - General Configuration.
 * Define which participant statuses will block a re-registration to your
   events (e.g. rejected) and which roles you would like to assign to speakers.
-* Configure which default matcher profile you would like to use (XCM-Extension)
+* Configure which default matcher profile you would like to use (XCM-Extension).
+  If using registration updates, make sure the XCM profile has the *Match
+  contacts by contact ID* activated, as otherwise duplicate contacts might be
+  created when updating event registrations.
 * Enter the urls to be used for registrations, modifications of registrations
   and cancellations which will depend on the external system you use. In case
   you use the CiviRemote Drupal module you may
@@ -157,4 +160,15 @@ behaviour of these calls:
    groups)
 
 ## Documentation
-- EN: https://docs.civicrm.org/remoteevent/en/latest (automatic publishing)
+- EN: https://docs.civicrm.org/remoteevent/en/latest (automatic publishing)
+
+## We need your support
+This CiviCRM extension is provided as Free and Open Source Software, and we are
+happy if you find it useful. However, we have put a lot of work into it (and
+continue to do so), much of it unpaid for. So if you benefit from our software,
+please consider making a financial contribution so we can continue to maintain
+and develop it further.
+
+If you are willing to support us in developing this CiviCRM extension, please
+send an email to [email protected] to get an invoice or agree a different payment
+method. Thank you!