Document webhook prerequisite in codemagic.yaml

Cutting v0.1.3 pushed the tag but no build started: the repo had no
webhook delivering events to Codemagic, so the tag trigger never fired.
Note that the triggering block alone is not enough and explain the two
ways to wire delivery (GitHub App or a manual repo webhook).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

codemagic.yaml

@@ -18,6 +18,17 @@
 #   2. Create an environment variable group named `appstore_connect` containing
 #      APP_STORE_APP_ID = the numeric Apple ID of the app record in
 #      App Store Connect.
+#   3. Make sure GitHub actually delivers events to Codemagic, or the `tag`
+#      trigger below never fires (the tag push is pushed into the void and no
+#      build starts). The `triggering` block alone is NOT enough. Either:
+#        - install the Codemagic CI/CD GitHub App and grant it this repo
+#          (https://github.com/settings/installations), or
+#        - add the app's webhook URL (from the Codemagic app's Webhooks page)
+#          to the repo: Settings -> Webhooks, content type `application/json`,
+#          "push" events (tag pushes arrive as push events).
+#      Verify a real tag push shows up under the Codemagic app's Webhooks
+#      deliveries; an empty `GET /repos/<owner>/<repo>/hooks` plus no GitHub
+#      App install means nothing is listening.
 
 workflows:
   ios-testflight: