[googledatastore] Update README.md for googledatastore.
[googledatastore] Update README.md for googledatastore.

madhurihn/YCSB_ToyDB,zyguan/ycsb,cricket007/YCSB,brianfrankcooper/YCSB,madhurihn/YCSB_ToyDB,leschekhomann/YCSB,zyguan/ycsb,jaemyoun/YCSB,leschekhomann/YCSB,ChristianNavolskyi/YCSB,zyguan/ycsb,leschekhomann/YCSB,manolama/YCSB,cricket007/YCSB,brianfrankcooper/YCSB,ChristianNavolskyi/YCSB,brianfrankcooper/YCSB,manolama/YCSB,ChristianNavolskyi/YCSB,ChristianNavolskyi/YCSB,manolama/YCSB,manolama/YCSB,jaemyoun/YCSB,cricket007/YCSB,cricket007/YCSB,brianfrankcooper/YCSB,madhurihn/YCSB_ToyDB,jaemyoun/YCSB,zyguan/ycsb,madhurihn/YCSB_ToyDB,leschekhomann/YCSB,jaemyoun/YCSB