Minor fixes.
Minor fixes.

I wanted to highlight just the App keyword, and specifying the plural involves either putting Apps as a keyword or App<space>s.
@danielskatz, could you take a quick look if this looks clean now please ? Here's how it looks on our doc pages:
http://parsl.readthedocs.io/en/latest/userguide/overview.html
Thanks!
swift-lang/swift-e-lab,Parsl/parsl,Parsl/parsl,swift-lang/swift-e-lab,Parsl/parsl,Parsl/parsl