added client secret param

Author: amirejaz

docs/toolhive/guides-cli/run-mcp-servers.mdx

@@ -664,6 +664,7 @@ thv run https://api.example.com/mcp \
   --name my-server \
   --remote-auth-issuer https://auth.example.com \
   --remote-auth-client-id my-client-id
+  --remote-auth-client-secret my-client-secret
 ```
 
 #### OAuth2 authentication