Make the README.md newbie (me-bie) first.

* Re-organized README so each section first speaks to theme and plugin
developers, the largest audiences, the audiences that benefit from a
little hand up.
* Introduced users to the shared filesystem.
* Tighted some of the language.
Keep the mission statement the same (for now)

Keep the 3 sentence/paragraph structure - wording changes ok
Be more explicit about WP directory locations in VVV

It may not be obvious that these directories are located in the
www directory of VVV
We haven't yet introduced `vagrant-local` as a concept

It may not make sense in the README quite yet. That said, the
getting started may move up in a bit here.c
Remove 'feel free' and suggest VVV as a learning environment
Update recommended Vagrant version to 1.6.x

Recommend Virtualbox 4.3.x rather than a specific patch release
Be a bit more explicit about the zip file process
Merge caveats with common caveats
Move Vagrant, VirtualBox descriptions to a requirements area

It should be clear that additional software needs to be installed
before VVV can work properly.
s/matchs/matches/
More around Vagrant and VirtualBox requirements
Swap VVV file system and scaffold sections
Move future of VVV to the bottom of the document
Link to a first vagrant up section in the quick start
Move shared file system text up again, don't provide a header

Modify the wording of the shared file system area
At this point you should be installing VirtualBox 4.3.x

Remove old Vagrant, VirtualBox version warning
Merge branch 'docs/readme'