Missing documentation for `deno check` tool

[glebbash]

I think it would be helpful to document deno check usage. I knew the command existed but it's usage is not that clear (including --help output).

I expected deno check to typecheck the whole project but it needs the file. Calling it like this deno check **/**.ts is also not what I was looking for. After some trial and error I figured out that it type-checks all of the imported files recursively so I basically needed to call deno check src/mod.ts.

Would be nice to clarify this in docs.

[thisisjofrank]

This now is documented here: https://docs.deno.com/runtime/reference/cli/check/