update prebuilt

contrib/prebuild-install/README.md

@@ -1,13 +1,10 @@
 ## Make use of pre-built images of Harbor
 
-Community members have helped building Harbor's docker images. If you want to save time from building Harbor from source. You can follow the below instructions to quickly pull Harbor's pre-built images for installation. 
-
-The script `docker-compose.sh` is used to change the registry service to pull pre-built images from. It updates `docker-compose.yml` to skip building the images from source locally.
-
+Community members have helped building Harbor's docker images. If you want to save time from building Harbor from source, please follow the below instructions to quickly pull Harbor's pre-built images for installation. 
 
 ### Steps
 
-Run the command update_compose.sh :
+Run the command `update_compose.sh` :
 ```
 $ ./update_compose.sh 
  
@@ -22,5 +19,5 @@ Enter **1** to pull images from Docker Hub,
 Enter **2** to pull image from Daocloud.io, recommended for Chinese users.  
 or Enter other registry URL like `https://my_registry/harbor/` . Do not forget the "/" and the end.
 
-This command will back up and update the file `Deploy/docker-compose.yml` . Next, just follow the [Harbor Installation Guide](../../docs/installation_guide.md) to install Harbor. 
+This command backs up and updates the file `Deploy/docker-compose.yml` . Next, just follow the [Harbor Installation Guide](../../docs/installation_guide.md) to install Harbor.