service/static-shim.md

@@ -111,6 +111,13 @@ This feature is automatically enabled when `static-shim-deploy.yml` is
 used. To opt-out of Review Apps, define `SKIP_REVIEW_APPS: 1` in the
 `variables` key of `.gitlab-ci.yml`.
 
+> Note that the `REVIEW_STATIC_GITLAB_SHIM_SSH_PRIVATE_KEY` needs to
+> be populated in the project for this to work. This is the case for
+> all projects under `tpo/web`. The public version of that key is
+> stored in Puppet's `hiera/common/staticsync.yaml`, in the
+> `review.torproject.net` key of the
+> `staticsync::gitlab_shim::ssh::sites` hash.
+
 The active environments linked to Review Apps can be listed by
 navigating to the project page in `Deployments` -> `Environments`.