Clean up minor issues with README

- Fix link to download community builds
- Remove "Welcome to" in header
- Remove "now open source" text
- Change "Download the source" to "Fork the source"
- Change Travis badge to the one directly from travis-ci.org
- Wrap prose on 80 characters
[skip ci]
Merge pull request #240 from Fryguy/cleanup_readme

Clean up minor issues with README