Add article for lazer-specific skin files

[Walavouchey]

example ppy/osu#32120 (reply in thread)

[Zyganadel]

Better yet, a separate section (or article) for what is/isnt skinnable in stable vs lazer.

[KOIRANNEKO]

I would make 2 sections - 1 is for stable skinning, and another for lazer skinning. Since lazer skinning is kinda different (for ex. no skinnable menu elements but more capabilities like custom ui elements wherever you want them etc.)