Add head shots to office hours host table

[kbeyls]

https://llvm.org/docs/GettingInvolved.html#office-hours documents all hosts hosting office hours.
It probably would help for some people to reduce anxiety on the first time dialing in if there were head shots for all of the hosts.

[llvmbot]

@llvm/issue-subscribers-infrastructure

[edward-jones]

After having a think after the round table I wonder whether there are other ways which might help make people more comfortable if a host doesn't want to put out a head shot. Maybe just some optional extra context about the person is sufficient, for example a role/workplace if they have one, a link to a personal blog/about page.