CmdPal: document how to properly log in an extension

### Describe the requested doc changes

I'm working on my first command palette extension and want to put some logging in place. I can't find any documentation for how to do that, and Copilot and Claude both seem to have made gibberish up.

It'd be nice to have an example or dedicated section that shows how to log from within an extension, and where to go to see those logs at runtime.