Repo setup tasks

[GroovinChip]

• Add info to CONTRIBUTING.md (branch structure, etc)
• Decide on lint rules and add them to analysis_options.yaml
• Decide on any actions and add them
• Decide on a pull request template and add it
• Decide on an issue template and add it

[GroovinChip]

Lint rules more or less addressed by #16 and #17

[GroovinChip]

Next up will be PR templates

[bdlukaa]

I'd be good to just follow dart conventions. (dartfmt)

[GroovinChip]

I'd like to have a checklist considering (at least)

• Addressed analyzer warnings as best as could be
• Dartfmt on all changed files
• Optimize imports on all changed files
• Documentation added/updated if applicable
• Version bump/changelog updated

Dartfmt/optimize imports could potentially be addressed in an Action? I'm still not great at those 😅

[GroovinChip]

Decided issue templates not necessary at this time.

Decided on https://github.com/marketplace/actions/dart-flutter-package-analyzer as an Action.