Add preliminary requirements mgmt docs

[gregshue]

The Zephyr Project is using the strictdoc tool for requirements management. The Zephyr Project is very early in the requirements management development process and has not settled on a requirements document tree - so there is no pattern to follow yet.

This ticket is to create a preliminary document tree to capture User/Stakeholder Needs and preliminary requirements on the BACnet-Stack project and on the BACnet-Stack deliverables (code).

[create-issue-branch]

Branch issue-15-Add_preliminary_requirements_mgmt_docs created!