New starter prescribing SQL tutorial

Current documentation:

• Getting started guide
• Some sample queries can be seen in this github issue tracker. In particular the "closed" issues (filter/tab at the top).
• Some jupyter notebooks. Not all of these query bigquery, so some will not be relevant.

How I suggest improving the documentation:

• The Getting Started Guide should be our primary source of documentation for the time being. Feel free to edit. Here's a guide on how to format text in github.
• As well as anything else you think is useful, I think it should include new sections with links to useful resources about:
  • Getting started with Jupyter Notebooks
  • introductory guide to sql. It should probably include a link to this guide to JOINs
• Most importantly, it should link to a new Jupyter notebook which showcases the best examples of sample queries taken from the issue tracker (and/or elsewhere)
• Remember, all queries need to remember to include the setting = 4 condition to exclude non-standard practices. (We should perhaps make a view for that, rather than having to remember to do it manually every time)