Handling of missing documents

[andrecedik]

I've tried to find out if this is just a bug, a missing feature, or something else. Since I wasn't "successful" here's a little description of what's been bugging me.

If you're using the CLI by running spectral lint and not adding a document/file name that should be checked, you receive the error message No documents provided. (among documentation of how to use the command). This is to be expected.

Unfortunately, if you provide a filename to a file that isn't available, maybe you're in the wrong folder or due to a typo (e.g. .ymlinstead of .yaml), you will receive an output that shows you how many rules have been found and how many of those are enabled. It also shows the message No results with a severity of 'error' found!.

It would be great if the user receives an error message that the file can't be found instead of returning a message that makes it seem that the document/file has been validated.