shared/contrib-additional.adoc: Add Chih-Hsin Chang

Chih-Hsin Chang works on porting OpenStack to FreeBSD.

His first commit in the main FreeBSD repositories is commit
01eb9d07cf92b70a890e4fe9264a6525ea8f299e in the doc repository, but
Chih-Hsin Chang had also submitted status reports earlier to the now
archived https://github.com/freebsd/freebsd-quarterly repository.

Approved by: carlavilla (mentor)
Differential Revision: https://reviews.freebsd.org/D39506