Finish the rest of the event documentation (#683)

doc/events/monitor_resize.md

@@ -0,0 +1,18 @@
+---
+module: [kind=event] monitor_resize
+---
+
+The @{monitor_resize} event is fired when an adjacent or networked monitor's size is changed.
+
+## Return Values
+1. @{string}: The event name.
+2. @{string}: The side or network ID of the monitor that resized.
+
+## Example
+Prints a message when a monitor is resized:
+```lua
+while true do
+  local event, side = os.pullEvent("monitor_resize")
+  print("The monitor on side " .. side .. " was resized.")
+end
+```