Added some documentation to the README
Added some documentation to the README


Former-commit-id: a475955c7763bf7daa4da1f570a855a2c0985444
clab/cnn,clab/dynet,shuheik/dynet,xunzhang/dynet,danielhers/dynet,shuheik/dynet,chunyang-wen/dynet,shuheik/dynet,danielhers/dynet,chunyang-wen/dynet,danielhers/dynet,shuheik/dynet,danielhers/dynet,clab/dynet,shuheik/dynet,chunyang-wen/dynet,xunzhang/dynet,xunzhang/dynet,xunzhang/dynet,clab/dynet,shuheik/dynet,clab/dynet,danielhers/dynet,clab/dynet,shuheik/dynet,clab/dynet,clab/cnn,danielhers/dynet,clab/dynet,clab/cnn,danielhers/dynet,chunyang-wen/dynet