Finish the rest of the event documentation (#683)

doc/events/paste.md

@@ -0,0 +1,18 @@
+---
+module: [kind=event] paste
+---
+
+The @{paste} event is fired when text is pasted into the computer through Ctrl-V (or ⌘V on Mac).
+
+## Return values
+1. @{string}: The event name.
+2. @{string} The text that was pasted.
+
+## Example
+Prints pasted text:
+```lua
+while true do
+  local event, text = os.pullEvent("paste")
+  print('"' .. text .. '" was pasted')
+end
+```