adding Will and Simon to reviewers/committers

[Colin Walters]

Hi,

I'd like to add

Will Thompson <will.thompson at collabora.co.uk>
Simon McVittie <simon.mcvittie at collabora.co.uk>

to the reviewer and committer list in HACKERS.  They've done a lot of
good work, and it'd help get their patches in if they had "official"
status here.  Unless there are any objections I'll add them today.