dreamcast_shelf: typo fix.
# Requires KallistiOS (KOS)
# http://gamedev.allusion.net/softprj/kos/
#
-# Tested on GNU/Linux, macOS and Windows (throught MinGW-w64/MSYS2, Cygwin and DreamSDK).
+# Tested on GNU/Linux, macOS and Windows (through MinGW-w64/MSYS2, Cygwin and DreamSDK).
# DreamSDK is based on MinGW/MSYS: https://dreamsdk.org/
#
# Input this command on the directory where mruby is installed:
