Update .gitignore to ignore IntelliJ project files, and to allow README files in db lib directories
Update .gitignore to ignore IntelliJ project files, and to allow README files in db lib directories

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