Update documentation and add pre-commit tooling

[VeckoTheGecko]

Changes:

• Update README
• Documentation
  • New homepage (with cards)
  • Roadmap page with embedded mindmap and link to discussion forum
  • New contributing guidelines (feedback welcome) with installation instructions
• Pre-commit tooling
• Removing requirements.txt
• Delete duplicate notebooks

There is still some room for improvement in the docs/readme in terms of copy-editing (e.g., the purpose of the project, and the direction of the project). Items in the documentation that require deeper thought, or require development beyond just documentation changes have been noted with TODO blocks.

[VeckoTheGecko]

Re. the duplicate notebooks, I ran a diff on them. None of the duplicate notebooks in Diagnostics were different to the tutorial ones (except small formatting details). I've gone ahead and deleted the duplicates in Diagnostics.

Also, is docs/tutorials going to be the home for the notebooks? Should I move the remaining ones to that folder?

Diagnostics/hex_labelling_demo.ipynb
Diagnostics/2DHistogram_method01.ipynb
Diagnostics/flock_diagnostics.ipynb

[VeckoTheGecko]

@sruehs and @LauraGomezNavarro any thoughts on these changes?