Remove non-extension API docs (#2877)

All documents that related to Lens IDE in general will move to the private lens-ide repository. All extension API documents will remain in the lens repository and be served on a new url.

Signed-off-by: Steve Richards <srichards@mirantis.com>

docs/README.md

@@ -1,21 +1,46 @@
-# Overview
+# Lens Extension API
 
-Lens is the most powerful Kubernetes IDE on the market. It is a standalone application, and it is available on macOS, Windows, and Linux. Some of the benefits of using Lens include:
+Customize and enhance the Lens experience with the Lens Extension API.
+Use the extension API to create menus or page content.
+The same extension API was used to create many of Lens's core features.
+To install your first extension you should goto the [extension page](lens://app/extensions) in lens.
 
-* Confidence that your clusters are properly setup and configured.
-* Increased visibility, real time statistics, log streams, and hands-on troubleshooting capabilities.
-* The ability to work with your clusters quickly and easily, radically improving productivity and the speed of business.
+This documentation describes:
 
-Watch this introductory video to see Lens in action:
+* How to build, run, test, and publish an extension.
+* How to take full advantage of the Lens Extension API.
+* Where to find [guides](extensions/guides/README.md) and [code samples](https://github.com/lensapp/lens-extension-samples) to help get you started.
 
-[![Screenshot](img/lens-intro-video-screenshot.png)](https://www.youtube.com/watch?v=eeDwdVXattc)
+## What Extensions Can Do
 
-**Note:** Use CTRL+click (on Windows and Linux) or CMD+click (on MacOS) to open the above in a new tab
+Here are some examples of what you can achieve with the Extension API:
+
+* Add custom components & views in the UI - Extending the Lens Workbench
+
+For an overview of the Lens Extension API, refer to the [Common Capabilities](extensions/capabilities/common-capabilities.md) page. [Extension Guides Overview](extensions/guides/README.md) also includes a list of code samples and guides that illustrate various ways of using the Lens Extension API.
+
+## How to Build Extensions
+
+Here is what each section of the Lens Extension API docs can help you with:
+
+* **Getting Started** teaches fundamental concepts for building extensions with the Hello World sample.
+* **Extension Capabilities** dissects Lens's Extension API into smaller categories and points you to more detailed topics.
+* **Extension Guides** includes guides and code samples that explain specific usages of Lens Extension API.
+* **Testing and Publishing** includes in-depth guides on various extension development topics, such as testing and publishing extensions.
+* **API Reference** contains exhaustive references for the Lens Extension API, Contribution Points, and many other topics.
+
+## What's New
+
+Just like Lens itself, the extension API updates on a monthly cadence, rolling out new features with every release.
+
+Keep up with Lens and the Lens Extension API by reviewing the [release notes](https://github.com/lensapp/lens/releases).
+
+## Looking for Help
+
+If you have questions for extension development, try asking on the [Lens Dev Slack](http://k8slens.slack.com/). It's a public chatroom for Lens developers, where Lens team members chime in from time to time.
+
+To provide feedback on the documentation or issues with the Lens Extension API, create new issues at [lensapp/lens](https://github.com/lensapp/lens/issues). Please use the labels `area/documentation` and/or `area/extension`.
 
 ## Downloading Lens
 
 [Download Lens](https://github.com/lensapp/lens/releases) for macOS, Windows, or Linux.
-
-## Quick Start
-
-Get up and running quickly by learning to [add clusters](clusters/adding-clusters.md).