fix(docs): align code block styles for shell snippets

[motorailgun]

What does this PR try to resolve?

Current contributor document has inconsistent styles for shell-command snippets, like with or without leading $. This PR removes all leading $ and specify bash for syntax highlighting, for the ease of copy-pasting commands.

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[epage]

I tend to lean towards console blocks for commands

[motorailgun]

Fair point as it feels shell-independent. Will fix those!

[motorailgun]

Umm, I thought so, but seems like bash blocks works better (in terms of syntax highlighting) for multi-line commands with comments like this. How do you think about that...?

[epage]

I've tended to do $ #. Not great but I feel its more semantically correct than describing these as bash scripts (which is what bash means). Unsure if others have other opinions.

[motorailgun]

That sounds fair, however for especially one-liner like this, I'd prefer the ease of copy-pasting by removing leading $:

cargo/src/doc/contrib/src/tests/writing.md

Lines 224 to 226 in f6cea42

	```console
	$ SNAPSHOTS=overwrite cargo test
	```

[epage]

I see that as a tooling limitation and I personally still lean towards console