Document ciadmin scope changes

docs/build-and-publish-pipeline.md

@@ -28,6 +28,10 @@ The key points:
         * Publish it to the [maven.mozilla.org](https://maven.mozilla.org).
 * Notifications about build failures are sent to a mailing list at
   [a-s-ci-failures@mozilla.com](https://groups.google.com/a/mozilla.com/forum/#!forum/a-s-ci-failures)
+* Taskcluster scopes are managed by the Release Engineering team using [ciadmin](https://hg.mozilla.org/ci/ci-admin/). The proper way to
+  add new scopes is to ask them on the `#releaseduty-mobile` Slack channel.
+  For testing or emergency, they can be modified directly on the [Taskcluster Scope Inspector](https://tools.taskcluster.net/auth/scopes/),
+  but when new `ciadmin` changes are applied, these changes will be lost.
 
 For Android consumers these are the steps by which Application Services code becomes available,
 and the integrity-protection mechanisms that apply at each step: