address some comments

Signed-off-by: Yi Wu <yiwu@pingcap.com>

.gitignore

 *.a
 *.o
 *.swp
+*_test
+titandb_bench
+titandb_stress
 
 build/
+.idea/
+.vscode/

README.md

 # Titan: A RocksDB Plugin to Reduce Write Amplification
 
-Titan is RocksDB Plugin for key-value separation, inspired by 
+Titan is a RocksDB Plugin for key-value separation, inspired by 
 [WiscKey](https://www.usenix.org/system/files/conference/fast16/fast16-papers-lu.pdf).
 For introduction and design details, see our
 [blog post](https://pingcap.com/blog/titan-storage-engine-design-and-implementation/).
 
 ## Build and Test
-Titan rely on RocksDB source code to build. You need to checkout RocksDB source code locally,
+Titan relies on RocksDB source code to build. You need to checkout RocksDB source code locally,
 and provide the path to Titan build script.
 ```
 # To build: