Remove Mozilla references from PROMOTION.md

Rewrite the PROMOTION.md file to be generic and applicable to all Hubs instances.
Removes the right for the owner of the instance to use the promoted scene in advertising without explicit consent.

Author: Exairnous

PROMOTION.md

@@ -1,3 +1,3 @@
 ## Scene Promotion
 
-As part of publishing your scene, you can choose to allow Mozilla to promote your scene. If you choose to allow Mozilla to promote your scene, you grant to Mozilla a non-exclusive, worldwide, royalty-free, sublicensable license under all of Your rights necessary to review your scene, and publish, distribute, and promote it as part of Hubs and Spoke or related Mozilla promotional efforts.
+As part of publishing your scene, you can choose to allow the Hubs instance owner to promote your scene. If you choose to allow the owner to promote your scene, you grant to the owner a non-exclusive, worldwide, royalty-free, sublicensable license under all of Your rights necessary to review your scene, publish it, and distribute it to the users of the Hubs instance.