Added devfile registry docs

docs/modules/user-guide/nav.adoc

@@ -1,4 +1,5 @@
 * xref:index.adoc[]
+* xref:devfile-registry.adoc[]
 
 * xref:authoring-stacks.adoc[]
 ** xref:adding-schema-version-to-a-devfile.adoc[]

docs/modules/user-guide/pages/devfile-registry.adoc

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+:description: Devfile Registry
+:navtitle: devfile-registry
+:keywords: devfile
+// :page-aliases:
+
+include::partial$con_devfile-registry.adoc[]

docs/modules/user-guide/partials/con_devfile-registry.adoc

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+[id="devfile-registry_{context}"]
+= Devfile registry
+
+[role="_abstract"]
+A devfile registry is a service that stores and provides devfile stacks to Kubernetes developer tools like odo, Eclipse Che, and the OpenShift Developer Console. Therefore, you can access devfiles through the devfile registry.  Devfile registries are based on the Oracle Cloud Infrastructure (OCI) Specification, and devfile stacks are stored as OCI-artifacts in the registry.
+
+Each devfile stack corresponds to a specific runtime or framework, such as Node.js, Quarkus, or WildFly. A devfile stack also contains resources like a `devfile.yaml` file, logo, and outer loop resources. Outer loop runs on containers and entails code reviews and integration tests, typically automated by continuous integration/continuous delivery (CI/CD) pipelines. These devfile stacks provide developers with templates to get started developing cloud-native applications.
+
+== Devfile registry components
+
+A devfile registry has two components:
+
+ * Devfile index server
+ * OCI registry server
+
+.Devfile index container
+
+The devfile index container image does the following actions:
+
+* Uses the `index.json` file to obtain metadata about the stacks and samples and hosts this metadata in the registry for tools to consume.
+* Bootstraps the OCI registry with the devfile stacks.
+* Provides an API to interact with the OCI registry and to retrieve devfile stacks.
+
+.OCI registry
+
+The devfile stacks in a devfile registry are stored in an OCI-compatible artifact registry. The artifact registry is based on the reference implementation of an OCI registry.
+
+When a devfile registry is deployed, the stacks belonging to the devfile registry are pushed to the OCI registry as multi-layer artifacts.
+
+== Types of devfile registries
+
+There are multiple types of devfile registries to access devfile stacks and tools.
+
+.Public community registry
+
+The public community registry provides stacks for various community tools to consume, such as Node.js, Quarkus, and Open Liberty.
+
+Locate the source for the stacks in the public community registry in the link:https://github.com/devfile/registry[devfile/registry repository].
+
+.On-cluster devfile registry
+
+Devfile registries can be operated on private Kubernetes clusters, deployed using either the devfile registry Operator or the devfile registry Helm Chart.
+
+The on-cluster devfile registries can be configured with custom devfile stacks suited to the needs of the owner organization.
+
+== Additional resources
+
+* xref:authoring-stacks.adoc[].