add brief explanation to warning in paste-URL-to-shorten prompt
add brief explanation to warning in paste-URL-to-shorten prompt

miguelfreitas/twister-html,xeddmc/twister-html,myleneb/twister-html,myleneb/twister-html,majestrate/twister-html,xeddmc/twister-html,slr/twister-html,majestrate/twister-html,miguelfreitas/twister-html,slr/twister-html