README Cleanup

Standard README cleanup (porting to markdown, inclusion of product photo with links to product, etc.)

Notable changes:

1. Added default CC by SA 3.0 license information. Please correct if this is not the right license for this repo.
2. Updated "Installation" section (which is now called "Getting Started" since the first step involves "Installation" of the IDE). Most notably we were instructing users to download a static zip file that's not being updated instead of the source code that they're looking at by being on this page. Download steps now detail cloning the repository as the primary method and downloading the repository as a zip file as an alternate method - both of which will fetch the current state of the example sketches.