Add a directory for design documents

Add a new directory, which I'm currently dubbing "Features", in
which will live design documents - descriptions of Podman
features that will be implemented or are being implemented.
Add a README and template to this directory to make the purpose
clear and enable easy addition of new design documents.

Signed-off-by: Matt Heon <matthew.heon@pm.me>

contrib/design-docs/README.md

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+## Design Documents
+
+This directory contains design information for Podman features that are being worked on or will be worked on in the future.
+All documents in this directory should be based on the [template](./TEMPLATE.md) provided.
+It is encouraged, but not required, that major features be preceded by a design document.
+This is intended to ensure major design changes are agreed to by maintainers before they are made.
+By discussing before implementing, we hope to avoid late-breaking issues discovered during code review that require rewrite of the feature.
+
+Design documents should be posted in pull requests that clearly indicate they are a design document, and should include only the design document, with no other code or other changes.
+The pull request should remain open for at least 1 week for comment before it is merged. Maintainers for the component the design document refers to should be pinged on the pull request and encouraged to comment with their opinions.
+Once committed, the design is considered to be finalized.
+This does not mean changes cannot be made, but given a design has already been agreed to, the bar required to force changes has raised substantially.
+Design documents should be removed once the feature they reference is implemented.
+Removed documents remain in the Git history if they need to be referenced in the future.

contrib/design-docs/TEMPLATE.md

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+# Change Request
+
+<!--
+This template is used to propose and discuss major new features to be added to Podman, Buildah, Skopeo, Netavark, and associated libraries.
+The creation of a design document prior to feature implementation is not mandatory, but is encouraged.
+Before major features are implemented, a pull request should be opened against the Podman repository with a completed version of this template.
+Discussion on the feature will occur in the pull request.
+Merging the pull request will constitute approval by project maintainers to proceed with implementation work.
+When the feature is completed and merged, this document should be removed to avoid cluttering the repository.
+It will remain in the Git history for future retrieval if necessary.
+-->
+
+## **Short Summary**
+
+<!--
+One to two sentence description of the proposal
+-->
+
+## **Objective**
+
+<!--
+What is this proposal trying to solve?
+Why is it necessary?
+-->
+
+## **Detailed Description:**
+
+<!--
+How should the feature be implemented?
+What considerations are there for the project if this is done?
+-->
+
+## **Use cases**
+
+<!--
+One or more short descriptions of use cases of the feature once complete.
+-->
+
+## **Target Podman Release**
+
+<!--
+When is this feature expected to be completed here?
+Are there hard deadlines to be aware of?
+-->
+
+## **Link(s)**
+
+<!--
+A list of links to relevant context.
+This can include Github issues describing the problem, related previous pull requests, or any other links that assist in understanding this change.
+The use of non-Github issue trackers - e.g. corporate or distribution Jira or Bugzilla instances - is allowed, but we ask that all links here be publicly accessible to ensure full context is available to all.
+Including a description with each link is not mandatory but is encouraged.
+-->
+
+## **Stakeholders**
+
+<!--
+A list of stakeholders who will be affected by this change.
+Please check any boxes that apply.
+For non-obvious stakeholders, you can add a brief sentence justifying after the checklist, but this is purely optional.
+-->
+- [ ] Podman Users
+- [ ] Podman Developers
+- [ ] Buildah Users
+- [ ] Buildah Developers
+- [ ] Skopeo Users
+- [ ] Skopeo Developers
+- [ ] Podman Desktop
+- [ ] CRI-O
+- [ ] Storage library
+- [ ] Image library
+- [ ] Common library
+- [ ] Netavark and aardvark-dns
+
+## ** Assignee(s) **
+
+<!--
+These people will lead implementation of the feature and drive it to completion.
+This does not have to be a comprehensive list of everyone who will work on the feature, but instead just the technical lead or leads.
+-->
+
+## **Impacts**
+
+### **CLI**
+
+<!--
+Will there be any impact to the CLI?
+Do any options need to be added?
+Mocked output is strongly encouraged to help demonstrate the changes.
+-->
+
+### **Libpod**
+
+<!--
+Will there be any changes to the core container management logic?
+-->
+
+### **Others**
+
+<!--
+Are there any major impacts not mentioned above?
+-->
+
+## **Further Description (Optional):**
+
+<!--
+Is there anything not covered above that needs to be mentioned?
+-->
+
+## **Test Descriptions (Optional):**
+
+<!--
+How will this feature be tested?
+Detail which existing test suite or suites will be used (or, if a new suite is required, why this is necessary and how it will be implemented.
+Will this change require changes to the CI images (e.g. the inclusion of new packages) to be tested?
+-->