Set up GitHub Actions Build for Linux

[Ujhhgtg]

Precisely, I do the following:

• capture build artifacts for linux
• upload these artifacts to releases
• update README for what i did

...and some small enhancements:

• suggests in readme that Arch Linux users can install QtScrcpy from AUR

These things are tested here

[Ujhhgtg]

I just found out that another pr is adding the arch linux suggestion, but that pr seems to...be in a mess. Thus it magically conflicts with the main repo :/

[Ujhhgtg]

Looks like it's because that fork is keep merging the new commits from the main repo, and cause that.

[Ujhhgtg]

Can some one review this?

[barry-ran]

Sorry I'm late. Great job