fix(doc): Update list of supported ddr versions

Apparently also forgotten to reflect currently
supported games.

Author: icex2

doc/ddrhook/ddrhook2.md

@@ -9,6 +9,8 @@ The following games are supported by this hook library:
 - Dance Dance Revolution 2013
 - Dance Dance Revolution 2014
 - Dance Dance Revolution A
+- Dance Dance Revolution A20
+- Dance Dance Revolution A20+
 
 Note that different builds of the same hook library are required to run the different versions. See
 different distribution packages, e.g. `ddr-12.zip`, `ddr-13.zip` etc.