Example Mixin being client-side only is error prone

[altrisi]

The example mixin (only one present) being client-side only (in client section) is error prone, given if you trust it to be the regular mixin array you may end up making part (or all) of your mod's functionality client-side only, being hard to debug if you don't stop to think that may be the issue.

Suggestion to change it to a mixin that applies on both sides.