MacOS/Windows: supports searching the entire disk

[mazzzystar]

This is a feature that I couldn't implement during the closed-source period. Currently, the Mac OS version only supports querying photos from the album. I hope to expand this to search for images across the entire disk.

As for Windows user, it should be entirely another app that could runs on Win system.

PR submissions are welcome.

[yudexiaozhou]

I think windows needs something similar

[mazzzystar]

@yudexiaozhou Thanks, would add it as a TODO.

[yujinqiu]

We have macOS version now: Searchable :-)

[mazzzystar]

@yujinqiu I've updated the README for Searchable.