CI: Travis: notify: hook: explain the current approach

M  .travis.yml

.travis.yml

@@ -156,6 +156,7 @@ notifications:
   webhooks:
     urls:
       - https://webhooks.gitter.im/e/b0312b18473340459d3e
+    # NOTE: Be silent about CI, until some PR started to pass CI succesfully.
     on_success: change
     # NOTE: `master` status in on the front page badge.
     on_failure: never