Update Bonus set naming guidelines (#309)

Adds a note about Bonus subset naming.

Co-authored-by: Matt Buchwald <mbuchwald@isquaredt.com>

Author: redwizard42

docs/guidelines/content/subsets.md

@@ -87,8 +87,13 @@ Restrictive challenges where player units or equivalent must never be used again
 
 A bonus set is a set with a variety of achievements that do not fit into the base set of a game for various reasons. These may be extremely difficult challenges that go beyond what is welcome, painful grinds that serve no particular purpose beyond getting stronger or collecting everything, a showcase of glitches, or many other kinds of things that wouldn't be considered good achievements for the base set.
 
+- Bonus sets should **not** be named `[Subset - Bonus]`. Instead, choose a name that fits thematically with the game to which this subset belongs.
 - A good example of the variety pack nature of a bonus set is the Suikoden Bonus Set, which contains various challenge runs, rare drops, and extreme challenges within a single subset.
 
+::: warning TIP
+Choose a name that fits thematically with the game.
+:::
+
 ## Naming Scheme
 
 To prevent players from getting confused, there is a specific naming scheme required for all Subsets: