change module name

README.md

-qrencode
+lua-resty-qrencode
 ==========
 
-## qrencode is a wrapper of libqrencode with libpng for OpenResty(nginx_lua).
+## lua-resty-qrencode is a wrapper of libqrencode with libpng for OpenResty(nginx_lua).
 
-qrencode is a wrapper of [libqrencode](http://fukuchi.org/works/qrencode/) with libpng for lua.
+lua-resty-qrencode is a wrapper of [libqrencode](http://fukuchi.org/works/qrencode/) with libpng for lua.
 
 ## Install
 
-qrencode is dependent on [libqrencode](http://fukuchi.org/works/qrencode/)
+lua-resty-qrencode is dependent on [libqrencode](http://fukuchi.org/works/qrencode/)
 and [libpng](http://www.libpng.org/pub/png/libpng.html), so make sure these are installed
 before compile it.