updated README
updated README

Added pointer to the API documentation.

jwise/libmpdclient,OpenInkpot-archive/iplinux-libmpdclient,cmende/libmpdclient,yusiwen/libmpdclient,yusiwen/libmpdclient,sl0th/libmpdclient,jagleeso/libmpdclient,yusiwen/libmpdclient,sl0th/libmpdclient,psych0tik/libmpdclient2,OpenInkpot-archive/iplinux-libmpdclient,psych0tik/libmpdclient2,jagleeso/libmpdclient,jwise/libmpdclient,jwise/libmpdclient,cmende/libmpdclient,jagleeso/libmpdclient,cmende/libmpdclient,sl0th/libmpdclient