guide on uptime and availability
Initial sweep
Fix typo

Wikipedia calls it 'oriented' rather than 'orientated'. That's not
definitive, but seems more common.
Case and hyphen

"Service Oriented Architecture" -> "service-oriented architecture".

I think we should retain the Americanism, since that's what people will
encounter on the wider internet. I agree with @sarahrichards that it
should be properly hyphenated though, my bad for not picking up on that.

I've not found anywhere that Martin Fowler has talked about
orient/orientate though :)
Minor spelling fixes
Fix plurality
Fix context
Merge pull request #164 from alphagov/uptime

guide on uptime and availability