Clarify location of foreign key.

This behavior surprised some of us coming from hibernate.

Perhaps the root problem was that I didn't know to look here: 
http://sequelize.readthedocs.org/en/latest/api/associations/#hasonetarget-options

docs/docs/associations.md

@@ -15,7 +15,9 @@ Project.hasOne(User)
   Furthermore, Project.prototype will gain the methods getUser and setUser according
   Furthermore, Project.prototype will gain the methods getUser and setUser according
   to the first parameter passed to define. If you have underscore style
   to the first parameter passed to define. If you have underscore style
   enabled, the added attribute will be project_id instead of ProjectId.
   enabled, the added attribute will be project_id instead of ProjectId.
- 
+  
+  The foreign key will be placed on the users table.
+  
   You can also define the foreign key, e.g. if you already have an existing
   You can also define the foreign key, e.g. if you already have an existing
   database and want to work on it:
   database and want to work on it:
 */
 */