feat: add section "gzip: invalid header"

Troubleshooting when
GitRepo complains with `gzip: invalid header`

docs/troubleshooting.md

@@ -210,3 +210,13 @@ You will need to re-import and restart the registration process: Select **Cluste
 
 !!! note "WaitCheckIn status for Rancher v2.5"
     The cluster will show in `WaitCheckIn` status because the `fleet-controller` is attempting to communicate with Fleet using the Rancher service IP. However, Fleet must communicate directly with Rancher via the Kubernetes service DNS using service discovery, not through the proxy. For more, see the [Rancher docs](https://rancher.com/docs/rancher/v2.5/en/installation/other-installation-methods/behind-proxy/install-rancher/#install-rancher). 
+
+### GitRepo complains with `gzip: invalid header`
+
+When you see an error like the one below ...
+
+```sh
+Error opening a gzip reader for /tmp/getter154967024/archive: gzip: invalid header
+```
+
+... the content of the helm chart is incorrect. Manually download the chart to your local machine and check the content.