Please add instructions for building on Linux

[FriederHannenheim]

No description provided.

[ambrosiogabe]

This is only supported on Windows right, now. I've updated the readme with this information.

[ThatOneCalculator]

If it is only on Windows, then why would you include Linux package manager instructions in the readme? Step 5 says to use Pacman, the Arch Linux package manager (see below screenshot)

[ambrosiogabe]

@ThatOneCalculator Yes, this is using pacman through msys2 since it's the only way to compile ffmpeg on Windows. It's like Wine on Linux, except it's the Wine for running linux on Windows.

It's part of the build instructions for ffmpeg for native compilation on Windows. Some helpful folks are working on adding Linux support though, so I'll be adding some additional information in the next week or so :)