tmplr on a repo without a recipe displays an error

[loreanvictor]

the docs claim that tmplr can be used on any repository, but using it on a repository without a recipe throws an error (since .tmplr.yml file can't be found).

I would recommend adding a few features to help alleviate this:

• [x] an expression to check if a file exists
• [x] a command to display a message (waiting for user confirm)
• [x] update degit-and-run recipe to check if .tmplr.yml exists, and if not, display a message instead.

[loreanvictor]

this is resolved via 8ce8644. no "inform" command was added, as prompt was usable for that purpose.