Update README with two caveats for Mac builds (case-insensitive FS and linker OOM with noopt).
Fixing formatting in README.md.
Removing TODOs accidentally left in README.
Merge pull request #255 from jlebar/readme-updates

Update README with two caveats for Mac builds (case-insensitive FS and l...
Merge branch 'master' of https://github.com/mozilla-b2g/B2G
Merge branch 'master' of https://github.com/svic/B2G