[Docs] Improve ExecuteC() documentation

[im-varun]

Hello!

The current documentation for the ExecuteC() method (on https://pkg.go.dev/github.com/spf13/cobra) simply states:
"ExecuteC executes the command."

It would be helpful to expand on this a bit further by providing a brief explanation of how ExecuteC() differs from Execute() in terms of its purpose and return values.

I'd be happy to submit a pull request if anyone has suggestions for how the ExecuteC() documentation could be improved.

Thanks.