Add a password for backup user

Otherwise backup user cannot login.

Guides/postgres.md

@@ -10,7 +10,9 @@ Create backup profile :
 CREATE ROLE backup WITH 
     NOSUPERUSER
     NOCREATEDB
-    NOCREATEROLE ;
+    NOCREATEROLE 
+    LOGIN
+    PASSWORD 'IWantToBackUp';
 ```
 
 Use `\du` to list roles.