Platform/Intel: Update Readme.md to point to edk2-non-osi master branch

Updated Platform/Intel/Readme.md to point to master branch on
edk2-non-osi instead of devel-MinPlatform

Updated edk2-platforms/Readme.md to point to Platform/Intel/Readme.md
for build instructions on Intel based Minimum Platforms

Added a link to the EDK II Minimum Platform Draft Specification
to Platform/Intel/Readme.md

Cc: Andrew Fish <afish@apple.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Michael Kubacki <michael.a.kubacki@intel.com>
Cc: Ankit Sinha <ankit.sinha@intel.com>
Cc: Chasel Chiu <chasel.chiu@intel.com>
Signed-off-by: Nate DeSimone <nathaniel.l.desimone@intel.com>
Reviewed-by: Chasel Chiu <chasel.chiu@intel.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Michael Kubacki <michael.a.kubacki@intel.com>