Add list of toolchain components to README (#3108)

* Add list of toolchain components to README

README.md

@@ -19,11 +19,46 @@ See [the rationale](https://kpt.dev/guides/rationale) for more background.
 The best place to get started and learn about specific features of kpt is 
 to visit the [kpt website](https://kpt.dev/).
 
-### Install kpt
+## Install kpt
 
 kpt installation instructions can be found on 
 [kpt.dev/installation](https://kpt.dev/installation/)
 
+## kpt components
+
+The kpt toolchain includes the following components:
+
+- **kpt CLI**: The [kpt CLI](https://kpt.dev/reference/cli/) supports package and function operations, and also
+  deployment, via either direct apply or GitOps. By keeping an inventory of deployed resources, kpt enables resource pruning,
+  aggregated status and observability, and an improved preview experience.
+
+- **Function SDKs**: Any general-purpose or domain-specific language can be used to create functions to transform and/or validate
+  the YAML KRM input/output format, but we provide SDKs to simplify the function authoring process, in 
+  [Go](https://kpt.dev/book/05-developing-functions/02-developing-in-Go), 
+  [Typescript](https://kpt.dev/book/05-developing-functions/03-developing-in-Typescript), and 
+  [Starlark](https://catalog.kpt.dev/starlark/v0.2/), a Python-like embedded language.
+
+- **Function catalog**: A [catalog](https://catalog.kpt.dev/) of off-the-shelf, tested functions. kpt makes configuration
+  easy to create and transform, via reusable functions. Because they are expected to be used for in-place transformation,
+  the functions need to be idempotent.
+
+- **Package orchestrator**: 
+  The [package orchestrator](https://github.com/GoogleContainerTools/kpt/blob/main/docs/design-docs/07-package-orchestration.md)
+  enables the magic behind the unique WYSIWYG experience. It provides a control plane for creating,
+  modifying, updating, and deleting packages, and evaluating functions on package data. This enables operations on packaged resources
+  similar to operations directly on the live state through the Kubernetes API.
+
+- **Config Sync**: While the package orchestrator
+  can be used with any GitOps tool, Config Sync provides a reference GitOps implementation to complete the WYSIWYG management
+  experience and enable end-to-end development of new features, such as 
+  [OCI-based packages](https://github.com/GoogleContainerTools/kpt/issues/2300). Config Sync is also helping to drive improvements
+  in upstream Kubernetes. For instance, Config Sync is built on top of [git-sync](https://github.com/kubernetes/git-sync) and
+  leverages [Kustomize](https://kustomize.io) to automatically render manifests on the fly when needed. It uses the same apply
+  logic as the kpt CLI.
+
+- **Backstage UI plugin**: We've created a proof-of-concept UI to demonstrate the WYSIWYG experience that's possible on top of the
+  package orchestrator. More scenarios can be supported by implementing form-based editors for additional Kubernetes resource types.
+
 ## Roadmap
 
 You can read about the big upcoming features in the