Update READE to add know issue for golang debug

[morningspace]

Describe in detail the problem you had and how this PR fixes it

This is a doc change to provide way to debug golang code using Go extension w/ code-server. Additional option is required when launch the code-server image.

Is there an open issue you can link to?

#725

[deansheather]

I'd probably change this to:

To debug Golang using [ms-vscode-go extension](https://marketplace.visualstudio.com/items?itemName=ms-vscode.Go), you need to add `--security-opt seccomp=unconfined` to your `docker run` arguments when launching code-server with Docker. See [#725](https://github.com/cdr/code-server/issues/725) for details.

[deansheather]

Also, please sign your commits with PGP so we can merge them into the repo.

[morningspace]

Thanks @deansheather I've made the change according to your comments.