docfix: add boolean array as option for indexing with .iloc
resolves #8956 Trivial documentation addition of boolean array as option for .iloc

@cswarth can you update to the comments?
 not sure what you need for in an update - I was just getting back to this when you mail came in.  I'll modify other doc sections on `.iloc` as requested.    Do you think it worth mentioning in close proximity that boolean array indexers should span the full axis?   Personally prefer to document what is, not what might be.
 @cswarth their are 2 mentions of the iloc description (one at the very top and one where you modified). Need them both to be the same. Nothing additional is necessary w.r.t. what you wrote.
 merged via https://github.com/pydata/pandas/commit/7be0236fa56429ccdd98b26dd3ab115b31025cb2

thanks!
