add doc of player.commands

doc/API.md

@@ -106,6 +106,7 @@
       - [player.xp](#playerxp)
       - [player.displayXp](#playerdisplayxp)
       - [player.xpLevel](#playerxplevel)
+      - [player.commands](#playercommands)
     - [Events](#events-2)
       - ["connected"](#connected)
       - ["spawned"](#spawned)
@@ -681,6 +682,29 @@ Number from 0 to 1.0 representing the progress bar at the bottom of the player's
 
 Level of xp the player has. Set this with player.setXpLevel()
 
+#### player.commands
+
+Instance of the [Command](#flying-squidcommand) class.
+Here is an example to create a new command :
+```js
+player.commands.add({
+    base: 'hello',
+    info: 'print hello in the console',
+    usage: '/hello <pseudo>',
+    op: false,
+    parse(str)  {
+      const args=str.split(' ');
+      if(args.length!=1)
+        return false;
+
+      return {pseudo:args[0]};
+    },
+    action({pseudo}) {
+      console.log("Hello "+pseudo);
+    }
+});
+```
+
 ### Events
 
 #### "connected"