Improve the root README.md file

[tulipdexter]

For public consumption the main README for the repo could be more conversation and friendly.

If this repo is to be consumed more like a book, then it should be approachable and navigable.
With this in mind it may be worth adding a TOC to this page as well. Currently, it suggests starting at the house-style which takes you into /practices/, immediately disorientating the reader.