Improved the README to be prettier for GitHub

### What's New

* Big header image added to match site header
* The title and link at the top are now bigger
* Added a "Helping Out" section with donations/code contributing info
* Donation address QR code
* End User Notes section is more readable
* Fixed "JavaScript functions" licenses table

See changes: [My fork's branch](https://github.com/danbartram/peercoin-walletgenerator/blob/improved_readme/README.md)