Improve CLI documentation

[mattkime]

I see docs here - https://github.com/Galooshi/import-js/#command-line-tool - that shows how to pass arguments to a given command but it doesn't say what the commands do. I've figured out that goto resolves the import statement to the file where its defined but the others remain a mystery. Just curious if we could get more explanation.

[trotzig]

The docs for the CLI tool are thin, I agree. I’d be happy to accept a PR updating the readme file!

[mattkime]

What does word do? What does search do? (locate an import statement in a file?)