Add contributor guide

[tbunch1]

Created a guidelines document for the User Guide, containing some basic information on contributing.

What this PR does / why we need it: Adds a contribution guide for the User Guide with more in depth guidelines than were previously present.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged): Fixes #701

Special notes for your reviewer:

Checklist

This checklist is not enforcing, but it's a reminder of items that could be relevant to every PR. Approvers are expected to review this list.

• [ ] Design: A design document was considered and is present (link) or not required
• [ ] PR: The PR description is expressive enough and will help future contributors
• [ ] Code: Write code that humans can understand and Keep it simple
• [ ] Refactor: You have left the code cleaner than you found it (Boy Scout Rule)
• [ ] Upgrade: Impact of this change on upgrade flows was considered and addressed if required
• [ ] Testing: New code requires new unit tests. New features and bug fixes require at least on e2e test
• [ ] Documentation: A user-guide update was considered and is present (link) or not required. You want a user-guide update if it's a user facing feature / API change.
• [ ] Community: Announcement to kubevirt-dev was considered

Release note:

NONE

[kubevirt-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Once this PR has been reviewed and has the lgtm label, please assign jean-edouard for approval. For more information see the Kubernetes Code Review Process.

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Needs approval from an approver in each of these files: - **[OWNERS](https://github.com/kubevirt/user-guide/blob/main/OWNERS)** Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[kubevirt-bot]

Hi @tbunch1. Thanks for your PR.

I'm waiting for a kubevirt member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[kubevirt-bot]

Issues go stale after 90d of inactivity. Mark the issue as fresh with /remove-lifecycle stale. Stale issues rot after an additional 30d of inactivity and eventually close.

If this issue is safe to close now please do so with /close.

/lifecycle stale

[kubevirt-bot]

Stale issues rot after 30d of inactivity. Mark the issue as fresh with /remove-lifecycle rotten. Rotten issues close after an additional 30d of inactivity.

If this issue is safe to close now please do so with /close.

/lifecycle rotten