Better doc for lookup param in python
Better doc for lookup param in python


Former-commit-id: a8a0d47e0aee5507288520ae24d544974d6c1ff7
clab/cnn,xunzhang/dynet,shuheik/dynet,shuheik/dynet,danielhers/dynet,danielhers/dynet,clab/dynet,shuheik/dynet,danielhers/dynet,shuheik/dynet,xunzhang/dynet,chunyang-wen/dynet,clab/dynet,clab/dynet,shuheik/dynet,danielhers/dynet,clab/dynet,clab/dynet,clab/cnn,xunzhang/dynet,danielhers/dynet,shuheik/dynet,chunyang-wen/dynet,danielhers/dynet,clab/dynet,chunyang-wen/dynet,danielhers/dynet,shuheik/dynet,xunzhang/dynet,clab/cnn,chunyang-wen/dynet,clab/dynet