Add Difficulty to the wiki pages

Command-Reference.md

@@ -477,6 +477,9 @@ Modifies a world's variable
 #### Examples:
 `/mv modify set animals false`   
 `/mv modify set pvp true world`   
+`/mv modify set diff 0`   
+`/mv modify set diff hard world_extreme`   
+`/mv modify set respawn respawn_world death_world`   
 #### Aliases:
 `/mv modify set ...`   
 `/mvmodify set ...`   
@@ -503,6 +506,9 @@ The modify command lets you set the variables for your Multiverse worlds in game
   - This value can either be the Name of a world or the Alias of that world. Space CAN be used.
 * mode/gamemode - String
   - Sets the mode for all players in a world. Must be `creative` or `survival`
+* diff/difficulty - String/Integer
+  - Sets the difficulty of a world. You can use string or integers:
+  - Possible values are PEACEFUL - 0, EASY - 1, MEDIUM - 2, HARD - 3 
 
 See the [[World Properties]] page for more detail on these variables.