More adjustments to bug reporting document

Summary:
Ref T12922.

• Tell customers where to go at the top.
• Fix a couple minor things (e.g., don't advise users to reproduce on secure anymore).

Test Plan: Read carefully.

Reviewers: chad, avivey

Reviewed By: chad, avivey

Maniphest Tasks: T12922

Differential Revision: https://secure.phabricator.com/D18236