Move threat model doc to GitHub

Move threat model doc to GitHub
Spoofing is no because we do set up a pre-shared secret key (as displayed on the monitor DFD) to prevent spoofing.

Elevation of Privileges is no because OSSEC separates the users roles for its different processes to avoid providing more privileges than required as shown on the monitor DFD.  Agent Security [1]

[1] http://www.ossec.net/?page_id=169