Add steps to get lightning goroutine (#6001)

tidb-lightning/tidb-lightning-faq.md

@@ -348,3 +348,19 @@ This error occurs usually because the CSV data file does not contain a header (t
 [mydumper.csv]
 header = false
 ```
+
+## How to get the runtime goroutine information of TiDB Lightning
+
+1. If [`status-port`](/tidb-lightning/tidb-lightning-configuration.md#tidb-lightning-configuration) has been specified in the configuration file of TiDB Lightning, skip this step. Otherwise, you need to send the USR1 signal to TiDB Lightning to enable `status-port`.
+
+    Get the process ID (PID) of TiDB Lightning using commands like `ps`, and then run the following command:
+
+    {{< copyable "shell-regular" >}}
+
+    ```sh
+    kill -USR1 <lightning-pid>
+    ```
+
+    Check the log of TiDB Lightning. The log of `starting HTTP server` / `start HTTP server` / `started HTTP server` shows the newly enabled `status-port`.
+
+2. Access `http://<lightning-ip>:<status-port>/debug/pprof/goroutine?debug=2` to get the goroutine information.