docs: update delve information

[aschey]

I ran into a bit of difficulty trying to connect the VS Code debugger to the process spawned by dlv debug. I eventually figured out that delve defaults to its legacy protocol (version 1) by default which was causing compatibility issues with VS Code's Go integration. Delve's docs recommend using version 2 for all new development, so I think it makes sense to add that to the docs so people trying to integrate with IDEs hopefully don't run into the same compatibility issues. Also added a note about supplying the port so these commands can integrate with IDEs and shell scripts without having to figure out the port each time.