(Draft) Rework Playbook structure

DRAFT: this issue is in draft - we need to work through the details before work starts.

The Playbook should serve as a bridge between the duck book and our own NHSBSA standards / guidance. It should supplement rather than duplicate any of these existing resources.

The current structure was designed to support this goal:

|- Home
|- Reproducible
|- Assured
|- Transparent

But since the pages underneath each heading are the same as the duck book (e.g. Modular, Documented, etc), this hasn't had the desired effect.

We would like a structure that moves us away from simply duplicating the duck book. The proposal is to move towards a structure that looks like (TODO: sections need better names)

|- Home
|- Principles
|  |- Reproducible
|  |- Assured
|  |- Transparent   
|- Tips and Tricks, suggested Ways of Working
|- Tool-specific implementation

Each section within Principles would then be a compilation of the relevant info/links: for example, 'Reproducible' would reference multiple relevant sections in the duck book (parts of Modular, Documented, etc) and link to our own standards and guidance. This would make it harder to directly map the pages (e.g. Documented in duck book --> Documented in playbook) and should reduce duplication by focussing on the principles rather than the mechanisms.