new committer (src): Ahmad Khalifa (vexeduxr)
Complete steps 1-4 for new committers from the committer's guide:
- Add myself to doc/shared/authors.adoc
- Add myself to doc/shared/contrib-committers.adoc
- Add a news entry
- Add my PGP key
Approved by: imp (mentor)
Differential Revision: https://reviews.freebsd.org/D50821