ci: add Matrix notification

.drone.yml

@@ -30,3 +30,15 @@ steps:
       event:
         exclude:
           - pull_request
+
+  - name: notify
+    image: plugins/matrix
+    settings:
+      homeserver:
+        from_secret: matrix_homeserver
+      roomid:
+        from_secret: matrix_roomid
+      username:
+        from_secret: matrix_username
+      password:
+        from_secret: matrix_password