Add architecture entry point and roadmap change process

Adds ARCHITECTURE.md as a high-level, discoverable entry point to Velero's
architecture, goals, and use cases that links to velero.io and the design/
directory instead of duplicating content.

Expands ROADMAP.md from a single wiki link (which pointed at the stale
vmware-tanzu path) into a short description of how the roadmap is maintained,
and repoints the wiki link to velero-io.

Links ARCHITECTURE.md from the README so it is easy to find.

These docs address incubation-review feedback that Velero's goals,
architecture, and roadmap process were scattered across the website.

Signed-off-by: Shubham Pampattiwar <spampatt@redhat.com>

ARCHITECTURE.md

@@ -0,0 +1,42 @@
+# Velero Architecture
+
+This is a high-level entry point to Velero's architecture. It links to the
+authoritative material rather than duplicating it, so the details stay in one
+place and do not drift.
+
+## How Velero works
+
+Velero runs a server (a set of controllers) in your cluster and a command-line
+client that runs locally. Backups and restores are driven by Kubernetes custom
+resources and reconciled by the server. Volume data is moved by the built-in
+file-system backup and by the data mover, and object and volume snapshot
+operations are handled through provider plugins.
+
+For the full component overview, the backup and restore flows, and the object
+storage and snapshot model, see:
+
+- [How Velero works](https://velero.io/docs/main/how-velero-works/)
+- [Velero documentation](https://velero.io/docs/)
+
+## Goals
+
+Velero gives you tools to back up and restore your Kubernetes cluster resources
+and persistent volumes, on public cloud or on-premises. The primary use cases
+are:
+
+- Take backups of your cluster and restore in case of loss.
+- Migrate cluster resources to other clusters.
+- Replicate your production cluster to development and testing clusters.
+
+## Design proposals
+
+Accepted and proposed designs live in the [`design/`](design/) directory. New
+designs follow [`design/_template.md`](design/_template.md) and are reviewed
+through pull requests and the community meetings. Implemented designs are
+archived under [`design/Implemented/`](design/Implemented/).
+
+## Related documents
+
+- [Roadmap](ROADMAP.md)
+- [Governance](https://github.com/velero-io/.github/blob/main/GOVERNANCE.md)
+- [Contributing](https://github.com/velero-io/.github/blob/main/CONTRIBUTING.md)

README.md

@@ -25,6 +25,8 @@ Velero consists of:
 
 [The documentation][29] provides a getting started guide and information about building from source, architecture, extending Velero and more.
 
+For a high-level overview of Velero's components, goals, and design process, see [ARCHITECTURE.md](ARCHITECTURE.md).
+
 Please use the version selector at the top of the site to ensure you are using the appropriate documentation for your version of Velero.
 
 ## Troubleshooting

ROADMAP.md

@@ -1 +1,24 @@
-# Please go to the [Velero Wiki](https://github.com/vmware-tanzu/velero/wiki/) to see our latest roadmap, archived roadmaps and roadmap guidance.
+# Velero Roadmap
+
+Velero maintains its roadmap in the project wiki. The wiki holds the current
+roadmap, archived roadmaps from previous release cycles, and guidance on how
+roadmap items are proposed and prioritized.
+
+- [Velero Wiki roadmap](https://github.com/velero-io/velero/wiki/)
+
+## How the roadmap is maintained
+
+Roadmap items are driven by the community and the maintainers:
+
+- Larger features start as a design proposal in the [`design/`](design/)
+  directory, following [`design/_template.md`](design/_template.md). Proposals
+  are discussed on the pull request and in the community meetings before they
+  are accepted.
+- Feature requests and bugs are tracked as
+  [GitHub issues](https://github.com/velero-io/velero/issues).
+- Priorities are reviewed by the maintainers each release cycle and discussed in
+  the bi-weekly [community meetings](https://velero.io/community/), which are
+  open to everyone.
+
+Anyone can propose a roadmap item by opening an issue or a design proposal, or by
+raising it in a community meeting.