Update READE to add know issue for golang debug

Author: morningspace

README.md

@@ -55,6 +55,7 @@ How to [secure your setup](/doc/security/ssl.md).
 ### Known Issues
 
 - Creating custom VS Code extensions and debugging them doesn't work.
+- To debug golang using [Go extension](https://marketplace.visualstudio.com/items?itemName=ms-vscode.Go), `--security-opt seccomp=unconfined` is required when launch the code-server image. See issue [#725](https://github.com/cdr/code-server/issues/725) for details.
 
 ### Future
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