Some grammar and spelling fixes

The last 3 sentences on flat files don't make perfect sense to me.  Do you mean 'uncompressed' instead of unused in the last sentence?

Anyway, I saw a positive tweet* about this project and then realized the least I could do was fix up some spelling, etc in your README.

* https://twitter.com/project_fifo/status/546487067409383425
Merge pull request #1 from rseymour/patch-1

Some grammar and spelling fixes in README