Add CONTRIBUTING docs and resync with PR template

CONTRIBUTING.md

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+# How to Contribute
+
+DSpace is a community built and supported project. We do not have a centralized development or support team, but have a dedicated group of volunteers who help us improve the software, documentation, resources, etc.
+
+* [Contribute new code via a Pull Request](#contribute-new-code-via-a-pull-request)
+* [Contribute documentation](#contribute-documentation)
+* [Help others on mailing lists or Slack](#help-others-on-mailing-lists-or-slack)
+* [Join a working or interest group](#join-a-working-or-interest-group)
+
+## Contribute new code via a Pull Request
+
+We accept [GitHub Pull Requests (PRs)](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/creating-a-pull-request-from-a-fork) at any time from anyone.
+Contributors to each release are recognized in our [Release Notes](https://wiki.lyrasis.org/display/DSDOC7x/Release+Notes).
+
+Code Contribution Checklist
+- [ ] PRs _should_ be smaller in size (ideally less than 1,000 lines of code, not including comments & tests)
+- [ ] PRs **must** pass [ESLint](https://eslint.org/) validation using `yarn lint`
+- [ ] PRs **must** not introduce circular dependencies (verified via `yarn check-circ-deps`)
+- [ ] PRs **must** include [TypeDoc](https://typedoc.org/) comments for _all new (or modified) public methods and classes_. Large or complex private methods should also have TypeDoc.
+- [ ] PRs **must** pass all automated pecs/tests and includes new/updated specs or tests based on the [Code Testing Guide](https://wiki.lyrasis.org/display/DSPACE/Code+Testing+Guide).
+- [ ] If a PR includes new libraries/dependencies (in `package.json`), then their software licenses **must** align with the [DSpace BSD License](https://github.com/DSpace/dspace-angular/blob/main/LICENSE) based on the [Licensing of Contributions](https://wiki.lyrasis.org/display/DSPACE/Code+Contribution+Guidelines#CodeContributionGuidelines-LicensingofContributions) documentation.
+- [ ] Basic technical documentation _should_ be provided for any new features or configuration, either in the PR itself or in the DSpace Wiki documentation.
+- [ ] If a PR fixes an issue ticket, please [link them together](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue).
+
+Additional details on the code contribution process can be found in our [Code Contribution Guidelines](https://wiki.lyrasis.org/display/DSPACE/Code+Contribution+Guidelines)
+
+## Contribute documentation
+
+DSpace Documentation is a collaborative effort in a shared Wiki. The latest documentation is at https://wiki.lyrasis.org/display/DSDOC7x 
+
+If you find areas of the DSpace Documentation which you wish to improve, please request a Wiki account by emailing wikihelp@lyrasis.org.
+Once you have an account setup, contact @tdonohue (via [Slack](https://wiki.lyrasis.org/display/DSPACE/Slack) or email) for access to edit our Documentation.
+
+## Help others on mailing lists or Slack
+
+DSpace has our own [Slack](https://wiki.lyrasis.org/display/DSPACE/Slack) community and [Mailing Lists](https://wiki.lyrasis.org/display/DSPACE/Mailing+Lists) where discussions take place and questions are answered.
+Anyone is welcome to join and help others. We just ask you to follow our [Code of Conduct](https://www.lyrasis.org/about/Pages/Code-of-Conduct.aspx) (adopted via LYRASIS).
+
+## Join a working or interest group
+
+Most of the work in building/improving DSpace comes via [Working Groups](https://wiki.lyrasis.org/display/DSPACE/DSpace+Working+Groups) or [Interest Groups](https://wiki.lyrasis.org/display/DSPACE/DSpace+Interest+Groups).
+
+All working/interest groups are open to anyone to join and participate.  A few key groups to be aware of include:
+
+* [DSpace 7 Working Group](https://wiki.lyrasis.org/display/DSPACE/DSpace+7+Working+Group) - This is the main (mostly volunteer) development team. We meet weekly to review our current development [project board](https://github.com/orgs/DSpace/projects), assigning tickets and/or PRs.
+* [DSpace Community Advisory Team (DCAT)](https://wiki.lyrasis.org/display/cmtygp/DSpace+Community+Advisory+Team) - This is an interest group for repository managers/administrators. We meet monthly to discuss DSpace, share tips & provide feedback back to developers.