I started to build a package for setting up a VS2015 bot, and realized
I didn't really remember how the toolchain setup worked. So I wrote
a readme for this directory.

I see I will live to regret putting way too many "2013"s in various
places in these scripts. :/

R=dpranke@chromium.org
BUG=492774

Review URL: https://codereview.chromium.org/1150033010

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@295437 0039d316-1c4b-4281-b951-d872f2087c98