mpc: add PKG_LICENSE information

Signed-off-by: Ian Leonard <antonlacon@gmail.com>

sound/mpc/Makefile

@@ -14,6 +14,8 @@ PKG_RELEASE:=2
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.xz
 PKG_SOURCE_URL:=http://www.musicpd.org/download/mpc/0
 PKG_MD5SUM:=d4f37e7e6b32c804a870192d1eb86199
+PKG_LICENSE:=GPL-2.0+
+PKG_LICENSE_FILES:=COPYING
 PKG_MAINTAINER:=Ted Hess <thess@kitschensync.net>
 
 include $(INCLUDE_DIR)/package.mk