To kick off the efforts on modularization, this patch introduces a document
describing the goals and general principles of modular design as well as a brief
introduction on the current status of component/module decomposition.
A detailed assignment of source files to components will be added in the future.
v2 -> v3:
* Expand mailing list address in the doc
v1 -> v2:
* Add more description on complexity measures, cyclic dependency avoidance, and
the reverse dependency of boot on hypervisor initialzation.
* Fix typos.
Tracked-On: #1842
Signed-off-by: Junjie Mao <junjie.mao@intel.com>