Update README.md

README.md

@@ -38,13 +38,13 @@ OceanBase Database is under [MulanPubL - 2.0](https://license.coscl.org.cn/Mulan
 
 ## How to build
 
-#### debug mode
+### debug mode
 > sh build.sh debug --init --make
 
-#### release mode
+### release mode
 > sh build.sh release --init --make
 
-#### rpm packages
+### rpm packages
 > sh build.sh rpm --init && cd build_rpm && make -j16 rpm
 
 ## Contributing