Update ps example to use a non-root user

README.md

@@ -6,14 +6,14 @@ privileges. The program will not run as a child, like su and sudo, so we
 work around TTY and signal issues.
 
 
-```console
-$ docker run -it --rm alpine:edge su -c 'ps aux'
+```shell
+$ docker run -it --rm alpine:edge su postgres -c 'ps aux'
 PID USER TIME COMMAND
- 1 root  0:00 ash -c ps aux
- 12 root  0:00 ps aux
-$ docker run -it --rm -v $PWD/su-exec:/sbin/su-exec:ro alpine:edge su-exec  root ps aux
+ 1 postgres 0:00 ash -c ps aux
+ 12 postgres 0:00 ps aux
+$ docker run -it --rm -v $PWD/su-exec:/sbin/su-exec:ro alpine:edge su-exec postgres ps aux
 PID USER TIME COMMAND
- 1 root  0:00 ps aux
+ 1 postgres 0:00 ps aux
 ```
 
 ## Why reinvent gosu?