chore(docs): add missing decorator in examples (#1950)

Author: JustaSqu1d

docs/ext/commands/commands.rst

@@ -899,6 +899,7 @@ If you want a more robust error system, you can derive from the exception and ra
             return True
         return commands.check(predicate)
 
+    @bot.command()
     @guild_only()
     async def test(ctx):
         await ctx.send('Hey this is not a DM! Nice.')