Minor improvements to contributing guide

[dstansby]

• Highlight code with bash highlighting
• Fix highlighting in markdown code block
• Remove leading "$" in code blocks to make it easier to copy/paste commands
• Add quotes around [docs] so that the command works as intended in zsh.
• Remove open command in doc building section, as this command is only available on macOS.

TODO:

• Add unit tests and/or doctests in docstrings
• Add docstrings and API docs for any new/modified user-facing classes and functions
• New/modified features documented in docs/tutorial.rst
• Changes documented in docs/release.rst
• GitHub Actions have all passed
• Test coverage is 100% (Codecov passes)

[MSanKeys963]

How about instead of removing open _build/html/index.html, we add xdg-open for Linux?

[dstansby]

I'd be minded not to include because then there would have to be multiple commands for each OS, and I'm not sure there is even one for Windows?

[MSanKeys963]

Suggested change

	make html
	make html
	open _build/html/index.html #macos
	xdg-open _build/html/index.html #linux

Maybe something like this?

[dstansby]

Again, I it's best to leave out so there's code that works on all operating systems that you can just copy/paste.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.98%. Comparing base (559c2e3) to head (ffc76fa).
Report is 257 commits behind head on v3.

Additional details and impacted files

@@           Coverage Diff           @@
##               v3    #1712   +/-   ##
=======================================
  Coverage   99.98%   99.98%           
=======================================
  Files          38       38           
  Lines       14718    14718           
=======================================
  Hits        14716    14716           
  Misses          2        2           

[jhamman]

@dstansby - would you be willing to take another pass on this w.r.t. our v3 dev process (hatch, etc)?

[dstansby]

I think that would be sufficiently different (and I've never used hatch personally) to be worth rebasing this PR, so I'll close