Add package manager command for Alpine Linux

[Elara6331]

This PR adds a package manager command for Alpine Linux to the prerequisites section of Getting Started.

This list of dependencies has been tested via the itgui-git LURE package and is known to work.

I omitted the linux-headers dependency because it's needed on all distros but it seems not to be in any of the lists on the site, but that may just be because it's installed by default on those distros. If you'd like me to add it back, I can do that.

[andydotxyz]

I omitted the linux-headers dependency because it's needed on all distros but it seems not to be in any of the lists on the site, but that may just be because it's installed by default on those distros. If you'd like me to add it back, I can do that.

If it is required, and not installed, then it should be in the list. I didn't think we linked against the linux-headers, but could be mistaken?

[Elara6331]

Yeah, I got an error for linux/input.h, I'll add it then.

[Elara6331]

Done