su: reorder examples, simpler first. (#2732)

pages/common/su.md

@@ -2,14 +2,14 @@
 
 > Switch shell to another user.
 
-- Switch to user {{username}} (password required):
-
-`su {{username}}`
-
 - Switch to superuser (admin password required):
 
 `su`
 
+- Switch to user {{username}} (password required):
+
+`su {{username}}`
+
 - Switch to user {{username}} and simulate a full login shell:
 
 `su - {{username}}`