Update README.md

Author: Goose97

README.md

@@ -1,7 +1,7 @@
 ### Hướng dẫn cài đặt
 ```
 wget https://statics.pancake.vn/thanos-test/cakecloud-postgres-exporter.tar.gz
-tar cakecloud-postgres-exporter.tar.gz
+tar -xvf cakecloud-postgres-exporter.tar.gz
 cd cakecloud-postgres-exporter
 make project=<PROJECT_NAME> database_user=<USER> database_password=<PASSWORD> database_name=<DB_NAME> port=<PORT>
 ```