Merge pull request #59 from rocker-org/sandbox

Sandbox
added a note on making a quick start.
reword

@eddelbuettel, thanks for your feedback, here's an attempt to be more general, acknowledge multiple containers in the repo, direct the reader to the wiki, and give them a line they can use to get started immediately. What do you think?

I'm not sure of the best practice for starting a docker container, I'd welcome advice on suitable arguments to use for the casual tire-kicking first-timer rocker user. I saw `--rm -t -i ` in a few places in other issue threads on this repo, so that seemed like a good place to start.
Merge pull request #60 from benmarwick/patch-1

added a note on making a quick start.
split 'overview' and 'getting started'

Yes, I hesitated about merging the two sections, and your comment confirms that was a poor choice. Here they are separate again. In this PR, the 'getting started' section is distinct but still visible to the casual browser coming from twitter, etc., without a minimum of scrolling. Hope that helps!
Merge pull request #62 from benmarwick/patch-2

split 'overview' and 'getting started'
Merge pull request #64 from rocker-org/sandbox

Sandbox
Merge pull request #65 from rocker-org/sandbox

Sandbox