Meta: add instructions to build on alpine

[diegoiast]

Bored, and installed Alpine on my laptop. Now building the IDE.

So far I konw:

apk add build-base cmake qt6-qtbase-dev clang ninja git qt6-qtsvg-dev ccache

I can build. Installing the desktop file works (I copied the binary to ~/codepointer and run from terminal once - then installed the desktop file).

Problem: app image generation does not work.

[diegoiast]

... menu is tinted blue... about is also blue. But docks are green. Using "official" build. WEIRD.

[diegoiast]

Not strictly related, but if you want to use QtCreator, and debug - you cannot use lldb on Alpine. Its not compiled with python support, and QtCreator needs it. You will need to use apk add gdb.