Add a flag, equivalent to `diff -s`, to report that checked file is okay

[stdedos]

For new checks and feature suggestions

• [ ] https://www.shellcheck.net/ (i.e. the latest commit) currently gives no useful warnings about this
• [x] I searched through https://github.com/koalaman/shellcheck/issues and didn't find anything related

Here's a snippet or screenshot that shows the problem:

Any script that's okay

Here's what shellcheck currently says:

While https://www.shellcheck.net/ says "No issues detected", my local terminal doesn't say anything. I have no .shellcheckrc file installed.

Here's what I wanted or expected to see:

The out-of-the-box configuration (i.e. the one just executed in the terminal) should have that prompt by default.

It's "easier" to convince yourself that shellcheck did it's job in the terminal, similarly to the web interface

Moar info

In my .shellcheckrc, I have some stylistic warnings activated, so that issue didn't surface until now.

[stdedos]

@koalaman notice me senpai? 😕