Automatically use a different port

[sbddesign]

I ran npm start when I already had another React project running in another shell.

Actual outcome: a message like "There is another process using port 3000".

Expected outcome: a message like "There is another process using port 3000. Would you like to run on another port?"

[bnonni]

This is good feedback. I'll see if I can figure out how to get it the cli to auto pick the next port n+1