caffeinate: add -d and fix -i example (#16899)

* Update caffeinate.md

Add -d command to prevent display from sleeping (most useful one to know imo).

Remove `-s` because it functions like `-i` except that it only works while on AC power

Better description for `-i`

* Add colon to end of example

pages/osx/caffeinate.md

@@ -3,22 +3,22 @@
 > Prevent macOS from sleeping.
 > More information: <https://keith.github.io/xcode-man-pages/caffeinate.8.html>.
 
+- Prevent the display from sleeping:
+
+`caffeinate -d`
+
 - Prevent from sleeping for 1 hour (3600 seconds):
 
 `caffeinate -u -t {{3600}}`
 
-- Prevent from sleeping until a command completes:
+- Fork a process, exec "make" in it, and prevent sleep as long as that process is running:
 
-`caffeinate -s "{{command}}"`
+`caffeinate -i make`
 
 - Prevent from sleeping until a process with the specified PID completes:
 
 `caffeinate -w {{pid}}`
 
-- Prevent from sleeping (use `<Ctrl c>` to exit):
-
-`caffeinate -i`
-
 - Prevent disk from sleeping (use `<Ctrl c>` to exit):
 
 `caffeinate -m`