Platform/Intel/Readme.md: Content update

This change makes the following updates:
  1. Add SimicsOpenBoardPkg details.
  2. Update Python instructions to Python 3.x and mention
     Python 2.x deprecation.
  3. Add Linux build environment set up instructions.
  4. Update supported compiler and tool versions to newer versions tested.
     * Ubuntu build: 16.04.5 LTS to 18.04.1 LTS
     * iASL: 20160527 to 20190816
     * NASM: 2.11.08 to 2.12.02
  5. Update ClevoOpenBoardPkg details.
  6. Add instructions to build packages (e.g. AdvancedFeaturePkg).
  6. Update Planned Activities and Ideas sections.

Cc: Agyeman Prince <prince.agyeman@intel.com>
Cc: Dandan Bi <dandan.bi@intel.com>
Cc: Sai Chaganty <rangasai.v.chaganty@intel.com>
Cc: Chasel Chiu <chasel.chiu@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Ankit Sinha <ankit.sinha@intel.com>
Cc: Wei David Y <david.y.wei@intel.com>
Signed-off-by: Michael Kubacki <michael.a.kubacki@intel.com>
Reviewed-by: Chasel Chiu <chasel.chiu@intel.com>
Reviewed-by: Nate DeSimone <nathaniel.l.desimone@intel.com>