Merge pull request #470 from yonasstephen/master

Add more psql commands

postgresql.md

@@ -2,15 +2,21 @@
 title: PostgreSQL
 ---
 
+Replace anything within `<placeholder>` accordingly
+
 ### Console
 
-    $ psql
+    $ psql #logs in to default database & default user
+    $ sudo -u <rolename:postgres> psql #logs in with a particular user
 
 ### Commands
 
+ * Show roles: `\du`
  * Show tables: `\dt`
  * Show databases: `\l`
- * Show columns of a table: `\d table` or `\d+ table`
+ * Connect to a database: `\c <database>`
+ * Show columns of a table: `\d <table>` or `\d+ <table>`
+ * Quit: `\q`
 
 ### Creating database