Description of problem:

The default value of FEATURE_MAILING is true in the document, but in fact, it is false.

The path is "Chapter 15. Schema for Red Hat Quay configuration" -> "FEATURE_MAILING"

Version-Release number of selected component (if applicable):

3.5

How reproducible:

always

Actual results:

The description of `FEATURE_MAILING` in quay document is 

 * FEATURE_MAILING [boolean]: Whether emails are enabled. Defaults to True.                   
   * Example: True      

Expected results:

The default value should be false.