document files/dirs used by apk in man page
apk uses files spread across the system. To find these it is needed to dig through the source code.
For example I wasn't able to find info about /etc/apk/repositories.d/
and /etc/apk/commit_hooks.d/
without looking at the source.
I have seen other man pages listing the relevant files so it would be nice to have that for apk too.