ENH: updated wording based on @tswicegood's comments

> "Since conda is aware of binstar sean is a shortform of https://conda.binstar.org/sean” — reads oddly.  How ‘bout: conda knows how to interact with binstar.  Specifying the channel “sean” translates to https://conda.binstar.org/sean.
FIX: wording from @tswicegood's comments

> "In order to install conda packages on binstar” — “install conda packages from binstar”
fix: wording @tswicegood
ENH: wording @tswicegood
added description of the  --override arg

> Search example: What is the --override arg doing?
Merge branch 'two-page-layout' of github.com:Binstar/docs.binstar.org into two-page-layout