chore(quickstart): mention private pool caveats (#317)

Author: Ace Nassri

cloudbuild/quickstart.js

@@ -27,6 +27,10 @@ async function quickstart(
   // Creates a client
   const cb = new CloudBuildClient();
 
+  // Note: for Private Pools, you'll have to specify an API endpoint value
+  // For example:
+  // const cb = new CloudBuildClient({ apiEndpoint: '<YOUR_POOL_REGION>-cloudbuild.googleapis.com' });
+
   // Starts a build against the branch provided.
   const [resp] = await cb.runBuildTrigger({
     projectId,