.pytool: Add CISettings.py and Readme.md

.pytool: Add CISettings.py and Readme.md

https://bugzilla.tianocore.org/show_bug.cgi?id=2315

Add main python script for EDK II Continuous Integration (CI)
builds along with a Readme.md that provides a summary of the
packages, platforms, and checks performs during a CI build.

Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>