Update Forbidden artists.mdx (clarification)

Minor clarification edit.

Author: CatgirlFrostmoon

src/content/docs/Forbidden artists.mdx

@@ -15,7 +15,7 @@ tags:
 ---
 
 This page contains list of artists whose entries are not allowed to be created on VocaDB.
-Please use custom artists if any of these people are attached to a song in an auxiliary manner (i.e. as an illustrator).
+Please use custom artists if any of these people are attached to a song in an auxiliary, non-musical manner (i.e. as an illustrator).
 
 For **existing** artist entries, see the [content removal guidelines](/docs/content-removal-guidelines).