add more serialization info to README
add more serialization info to README


Former-commit-id: ac0e28536630530c07b34667139e426fb9e415dd
danielhers/dynet,clab/dynet,danielhers/dynet,shuheik/dynet,clab/dynet,clab/dynet,chunyang-wen/dynet,clab/dynet,shuheik/dynet,chunyang-wen/dynet,clab/cnn,danielhers/dynet,shuheik/dynet,shuheik/dynet,danielhers/dynet,danielhers/dynet,chunyang-wen/dynet,clab/cnn,clab/cnn,clab/dynet,danielhers/dynet,shuheik/dynet,xunzhang/dynet,clab/dynet,danielhers/dynet,chunyang-wen/dynet,xunzhang/dynet,clab/dynet,shuheik/dynet,xunzhang/dynet,shuheik/dynet,xunzhang/dynet