For a single input .ts file, imports in the .ts file cause an error, which does indicate what to do

[FranzZemen]

Not a showstopper, but would be helpful for new users.

Use case: I was generating .js file from a single .ts file. It failed with an ambiguous error. The file had imports, and I presumed that was the issue. The directory was self-containing i.e. .ts in this directory only imported from themselves or from node. So I used the directory option and that worked.

Fix suggested:

• Provide a more intuitive error message
• or Convert imports as well (or handle in some way)

[futurGH]

Definitely worth supporting imports, I think it makes more sense to track this on #15.