Updates to the ReadMe file

A bunch of updates to the read me file. Most of it is surface level
tweaking. I’ve also included instructions on how to get an API key, and
a few additional links to choice pages on developers.google.com.
Removing unnecessary markdown
Comments from macd

 - clarifying java version
 - lower case ‘keys’
 - small code change when setting your key
Small note about version 0.x.
Merge pull request #26 from googlemaps/readme-updates

Updates to the ReadMe. Cleaning up the original documentation, and clarifying some things around support/contribution.