add contributing file

[MrPowers]

Fixes #321

The CONTRIBUTING.md file is conventional in OSS repos. This one draws inspiration from the Rails CONTRIBUTING.md file.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #329   +/-   ##
=======================================
  Coverage        ?   74.03%           
=======================================
  Files           ?       43           
  Lines           ?     8137           
  Branches        ?     8137           
=======================================
  Hits            ?     6024           
  Misses          ?     1733           
  Partials        ?      380           

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[zachschuermann]

link slack channel?

[MrPowers]

We unfortunately can't provide a link cause Slack channel links die every 30 days 🙃

[zachschuermann]

or rather the slack workspace in general? can we have the overall slack workspace link?

[nicklan]

delta-users.slack.com right?

Suggested change

	Feel free to create an issue or join the Delta Lake Slack channel with questions!
	Feel free to create an issue or join the Delta Lake Slack channel (`#delta-kernel` on delta-users.slack.com) with questions!

[nicklan]

Thanks, this is great. lgtm, feel free to accept my slack channel suggestion if it makes sense, or something else if not. Probably good if we can give some way they can track down where the slack channel is.

[nicklan]

delta-users.slack.com right?

Suggested change

	Feel free to create an issue or join the Delta Lake Slack channel with questions!
	Feel free to create an issue or join the Delta Lake Slack channel (`#delta-kernel` on delta-users.slack.com) with questions!

[MrPowers]

@nicklan @zachschuermann - thanks for reviewing!

I added this Slack link: https://go.delta.io/slack

I checked and that's what's used on the delta.io site.

Let me know if you have any additional comments!