Add notes about github-apps

Signed-off-by: Tim Hansen <timbonicus@gmail.com>

docs/integrations/github/discovery.md

@@ -48,7 +48,8 @@ request for each discovered location.
 This means if you have more than ~140 catalog entities, you may get throttled by
 rate limiting. This will soon be resolved once catalog refreshes make use of
 ETags; to work around this in the meantime, you can change the refresh rate of
-the catalog in your `packages/backend/src/plugins/catalog.ts` file.
+the catalog in your `packages/backend/src/plugins/catalog.ts` file, or configure
+Backstage to use the [github-apps plugin](../../plugins/github-apps.md).
 
 This is true for any method of adding GitHub entities to the catalog, but
 especially easy to hit with automatic discovery.

docs/integrations/github/locations.md

@@ -56,3 +56,9 @@ You need to supply either `apiBaseUrl` or `rawBaseUrl` or both (except for
 public GitHub, for which we can infer them). The `apiBaseUrl` will always be
 preferred over the other if a `token` is given, otherwise `rawBaseUrl` will be
 preferred.
+
+## Authentication with GitHub Apps
+
+Alternatively, Backstage can use GitHub Apps for backend authentication. This
+has higher rate limits, and a clearer authorization model. See the
+[github-apps plugin](../../plugins/github-apps.md) for how to set this up.