Note undesired behavior from setting enabled: true in root project

[jtcohen6]

From dbt Slack:

A user had the following config in dbt_project.yml:

models:
 ...
 snowplow:
   enabled: true

Setting enabled: true in the root project overrides the dynamic, target-dependent enabled values set from within the snowplow package. Removing that line made this magically work again.

I don't think there's anything we could or should do to "lock" those enabled values within a package, since it's expected (and good) behavior that the user can override locally. What I will do is document that setting a top-level enabled config can have surprising results.

Reminder to self to add a note to the README :)