Update readme for 1.0

**We don't want to merge this until we're live with 1.0**
Instead of removing this section, should we wordsmith it into something like "Brackets is at 1.0, but we're not stopping there..."

And "So feel free to give it a spin and let us know what's still missing! Being built on JavaScript, it's easy to make your own changes, and we give priority to integrating your pull requests back into Brackets!"