Fix the Troubleshooting section with --display-uri

$ t authorize --display-url # This will not work. ☹
Unknown switches '--display-url'

$ t authorize --display-uri
Welcome! Before you can use t, you'll first need to register an
application with Twitter. Just follow the steps below:
Merge pull request #153 from tomer/patch-1

Fix the Troubleshooting section with --display-uri