update `requirements-write.txt`

The current requirements file is out of date and potentially too minimal

https://github.com/pymc-devs/pymc-examples/blob/dce63a03b894d39a0a39a4773f9a0226078391c1/requirements-write.txt#L1-L9

Todo

• Replace pymc3 with pymc, possibly with a >=4.0 version tag.
• We don't need to have total coverages of all packages used in the repo, but it would be helpful to add more commonly used packages such as:
  • matplotlib
  • numpy
  • xarray
  • seaborn
  • bambi
  • jupyterlab-code-formatter, isort (useful when writing notebooks in the browser, rather than VS Code for example)
  • patsy
  • scipy
  • daft (for making causal DAG's)
• Check version on pre-commit is still appropriate
• Update instructions in final section of the contributing guide to include the instructions on how to build a pymc-examples-env environment. E.g. conda create --name pymc-examples-env --file requirements-write.txt

Happy to take feedback on this of course.

Start with requirements-write.txt and the final section of CONTRIBUTING.md. Compare the listed dependencies and pre-commit version with the repository's current needs, then verify the documented conda create command. Done means the requested packages and PyMC entry are updated and the contributing instructions describe the pymc-examples-env setup.