uptime: fill out some more options (#2165)

pages/common/uptime.md

@@ -5,3 +5,15 @@
 - Print current time, uptime, number of logged-in users and other information:
 
 `uptime`
+
+- Show only the amount of time the system has been booted for:
+
+`uptime --pretty`
+
+- Print the date and time the system booted up at:
+
+`uptime --since`
+
+- Show version information:
+
+`uptime --version`