MFC [1] r278115, r278116:

MFC [1] r278115, r278116:

 r278115:
  Move the 'Upgrading from Previous Releases of FreeBSD'
  section to the top of the file, following the introduction.

 r278116:
  Overhaul the relnotes page to reorganize the sections.

  With the previous layout, the majority of the release
  notes were categorized under one main "What's New"
  section, which in addition to making the page difficult
  to parse relevant bits, also had a few rendering issues,
  such as 'Note' blocks visually not appearing as if they
  pertain to a particular change.

  This change removes the "What's New" section, integrating
  it with the introduction.  In addition, each section now
  provides a brief description of its contents, broken down
  further into a subsection for each "topic", making it much
  easier to find a specific topic in the page.

[1] This is a direct commit, not an MFC.

Sponsored by:	The FreeBSD Foundation

git-svn-id: svn://svn.freebsd.org/base/stable/10@278258 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f