Mention Wapcaplet requirement.
Mention Wapcaplet requirement.

svn path=/trunk/libcss/; revision=9134

zhuyadong/libcss,servo/libcss,servo/libcss,zhuyadong/libcss,servo/libcss,prepare/netsurf_libcss,zhuyadong/libcss,prepare/netsurf_libcss,prepare/netsurf_libcss