Fixes #2782 - Edit dev-env-setup.md around GH client ID/secret + typos

[laghee]

This PR fixes issue #2782

Proposed PR background

• Deletes sentence that claims webcompat org members can retrieve the GH client ID & secret from settings (which only org owners can access)
• Fixes some typos and formatting inconsistencies (some of these might be subjective)

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• [✅] I have read the Pull Request + Code Style Guidelines thoroughly.

[karlcow]

Thanks @laghee

different markdown style ;)

just one request to improve the list formatting.

[laghee]

different markdown style ;)

Oh, weird, you're right -- I didn't even notice that! Apparently my vscode markdown plugin is very aggressive about changes without explicit approval... how annoying. I think I can roll those back by mucking with settings if necessary.

[miketaylr]

ha, nice find.

[miketaylr]

I think I can roll those back by mucking with settings if necessary.

I'm not sure it really matters, as long as the end result is the same.

[karlcow]

let's go with it.