Add a getting started guide

[j-rewerts]

In Browsh issue #188, a user would like to host their own Browsh server. If we had a getting started guide, it could help these users get started a little easier.

[tombh]

Bare in mind that this repo isn't just for running a Browsh server, but for running Browsh at infinite scale! So a lot of the code here is designed to be able to support many thousands of concurrent users. So it's not likely to be relevant to the average user. That being said, there are definitely some relevant folders an lines of code that will be useful for users that do want a turn key solution for getting a long-lived SSH or HTTP Browsh service up and running.