Output all executed commands when --verbose and explain

[grayside]

When rig shells out to execute a command, we have a teaching moment to explain some piece of the stack. Output the command and provide a one-line explanation of what it does when --verbose is used.

This follows #4 for use of the --verbose flag.

[grayside]

After further thinking about this, I'm inclined to formalizing it with a separate flag entirely, --learning. Don't include the verbose output necessarily, do have yellow output or the like outputting the commands with messages on their use.

Commands that should show up here might be run with a StreamCommandLearning() method which has a final message parameter explaining what it does.