Finish the rest of the event documentation (#683)

doc/events/computer_command.md

@@ -0,0 +1,18 @@
+---
+module: [kind=event] computer_command
+---
+
+The @{computer_command} event is fired when the `/computercraft queue` command is run for the current computer.
+
+## Return Values
+1. @{string}: The event name.
+... @{string}: The arguments passed to the command.
+
+## Example
+Prints the contents of messages sent:
+```lua
+while true do
+  local event = {os.pullEvent("computer_command")}
+  print("Received message:", table.unpack(event, 2))
+end
+```