add max_size docs
add max_size docs

tomhughes/node-mapnik,CartoDB/node-mapnik,mapnik/node-mapnik,mapnik/node-mapnik,CartoDB/node-mapnik,mapnik/node-mapnik,tomhughes/node-mapnik,mapnik/node-mapnik,tomhughes/node-mapnik,mapnik/node-mapnik,tomhughes/node-mapnik,CartoDB/node-mapnik,CartoDB/node-mapnik,tomhughes/node-mapnik,CartoDB/node-mapnik