chore(docs): Update README with deprecation note (#383)

Because

- This repository will soon be deprecated and shouldn't take more
contributions.

This commit

- Adds a deprecation note before archiving it.

README.md

@@ -1,5 +1,21 @@
 # Component
 
+---
+
+## ⚠️  Deprecation of this repository
+
+This repository is in process of being moved to
+[`pipeline-backend`](https://github.com/instill-ai/pipeline-backend/tree/main/pkg/component).
+Please, update and import the code in / from that repository instead of this
+one.
+
+A few remaining tasks remain before archiving the repository:
+- [ ] Port the Pull Requests to `pipeline-backend`.
+- [ ] Move [`compogen`](./tools/compogen) to `pipeline-backend`.
+- [ ] Merge the contribution guidelines in the new repository.
+
+---
+
 A **component** is the basic building block of the [**Instill Core**](https://github.com/instill-ai/instill-core) pipeline. The pipeline consists of multiple components.
 We have two types of components: connectors and operators.
 This Golang package defines the common interface and functions for all components.