Update details about projects and manifest files

doc/user/clusters/agent/index.md

@@ -377,3 +377,18 @@ Alternatively, you can mount the certificate file at a different location and in
           mountPath: /tmp/myCA.pem
           subPath: myCA.pem
 ```
+
+#### Project not found
+
+```json
+{
+  "level ":"error ",
+  "time ":"2022-01-05T15:18:11.331Z",
+  "msg ":"GetObjectsToSynchronize.Recv failed ",
+  "mod_name ":"gitops ",
+  "error ":"rpc error: code = NotFound desc = project not found ",
+}
+```
+
+This error is shown if the manifest project is not public. To fix it,
+[make sure your manifest project is public](repository.md#synchronize-manifest-projects).

doc/user/clusters/agent/repository.md

@@ -40,6 +40,9 @@ with Kubernetes resource definitions in YAML or JSON format. The Agent monitors
 each project you declare, and when the project changes, GitLab deploys the changes
 using the Agent.
 
+WARNING:
+When using separate GitLab projects for manifest files and configuration repository, the manifests project must be public.
+
 To use multiple YAML files, specify a `paths` attribute in the `gitops.manifest_projects` section.
 
 ```yaml