Update README.md

Author: Goose97

README.md

@@ -2,6 +2,6 @@
 ```
 wget https://statics.pancake.vn/thanos-test/cakecloud-postgres-exporter.tar.gz
 tar -xvf cakecloud-postgres-exporter.tar.gz
-cd postgres-exporter
+cd postgres_exporter
 make project=<PROJECT_NAME> database_user=<USER> database_password=<PASSWORD> database_name=<DB_NAME> port=<PORT>
 ```