Add how-to connect postgre SQL database in CLI

Guides/postgres.md

@@ -2,6 +2,14 @@
 
 Tips for using Postgres SQL.
 
+## Use a database in a commandline
+
+```
+sudo service postgresql start ;
+sudo -u postgres psql <db name> ;
+sudo update-rc.d postgresql disable
+```
+
 ## Backup
 
 Create backup profile :