doc: add QA testing guideline (#303)

* doc: add testing guideline

Signed-off-by: Yi-Ya Chen <yiya.chen@suse.com>

* doc: update wording

Co-authored-by: Andy Lee <andy.lee@suse.com>
Signed-off-by: Yiya Chen <yiya.chen@suse.com>

---------

Signed-off-by: Yi-Ya Chen <yiya.chen@suse.com>
Signed-off-by: Yiya Chen <yiya.chen@suse.com>
Co-authored-by: Andy Lee <andy.lee@suse.com>

README.md

@@ -1,62 +1,93 @@
 # harvester-ui-extension
 
-Rancher Extension used in [rancher/dashboard](https://github.com/rancher/dashboard) for [Harvester](https://harvesterhci.io) Dashboard UI.
+The Harvester UI Extension is a Rancher extension that provides the user interface for [Harvester](https://harvesterhci.io) within the [Rancher Dashboard](https://github.com/rancher/dashboard).
 
-`
-From Rancher 2.10.0, Harvester integration is provided by this new Harvester UI Extension.
-`
+> **Note:**
+> This extension is available starting from **Rancher 2.10.0**. Ensure your Rancher version is **2.10.0 or later** to access Harvester integration.
 
 ## Installation
 
-To install the Harvester UI Extension in Rancher 2.10.0 and newer, please refer to [installation](https://docs.harvesterhci.io/v1.5/rancher/harvester-ui-extension#installation-on-rancher-210) on harvester doc.
+For detailed installation instructions, please refer to the [official Harvester documentation](https://docs.harvesterhci.io/v1.5/rancher/harvester-ui-extension#installation-on-rancher-210).
 
-## Running for Development
 
-This is what you probably want to get started.
-
-### Prerequisite
-
-Nodejs version >= 20
+## Development Setup
 
+Ensure **Node.js v20 or later** is installed for development and debugging.
 
 ### Standalone Mode
 
-For development, serve with hot reload at https://localhost:8005
+Run the extension standalone with hot reload at `https://localhost:8005`.
 
 ```bash
 # Install dependencies
 yarn install
 
-# Use RANCHER_ENV to specify the endpoint for your Harvester API
+# Start the development server
 RANCHER_ENV=harvester API=https://your-harvester-ip yarn dev
 
-# Use VUE_APP_SERVER_VERSION to specify the Harvester server version
-# in case your are running a dev build of Harvester
-RANCHER_ENV=harvester VUE_APP_SERVER_VERSION=your-harvester-server-version API=https://your-harvester-ip yarn dev
+# Example with specific server version
+RANCHER_ENV=harvester VUE_APP_SERVER_VERSION=v1.5.0 API=https://192.168.1.123 yarn dev
+```
 
-# or put your env variables into a .env file
+You may also define environment variables in a `.env` file:
 
-# Example
-RANCHER_ENV=harvester VUE_APP_SERVER_VERSION=v1.4.0 API=https://192.168.1.123 yarn dev
+```env
+RANCHER_ENV=harvester
+VUE_APP_SERVER_VERSION=v1.5.0
+API=https://192.168.1.123
 ```
 
 ### Rancher Integration Mode
 
-In this mode, you need to have Rancher and run Harvester UI Extension as Rancher extension, see more detail in [Rancher UI extension](https://extensions.rancher.io/extensions/next/extensions-getting-started#running-the-app).
+To run as a Rancher extension, follow the [Rancher UI Extension Guide](https://extensions.rancher.io/extensions/next/extensions-getting-started#running-the-app).
 
 ```bash
 API=https://your-rancher-ip yarn dev
-
-# Example
-API=https://192.168.1.123 yarn dev
 ```
 
+## Branch Structure
+
+- **`main`** – Main development branch
+- **`release-harvester-vX.Y`** – Stable release branches per version series
+- **`vX.Y-head`** – Testing branches for ongoing changes to extension builds in each release series
+
+> **Note:**
+> The `vX.Y-head` branches are auto-generated and kept in sync with release branches. Use these for testing the latest changes in each version series.
+
+## Testing Guidelines
+
+### UI Extension Testing
+
+To validate changes in a release series, switch to the appropriate `vX.Y-head` branch. For main branch testing, use `main-head`.
+
+- Examples:
+  - Test `1.0.x` series → `v1.0-head`
+  - Test `1.5.x` series → `v1.5-head`
+
+**Steps:**
+1. Navigate to **Rancher UI** → **Local** → **App** → **Repositories**
+2. Refresh the Harvester repository using the target `vX.Y-head` branch
+3. Go to the **Extensions** page and install the desired version
+
+### Standalone Mode Testing
+
+To test the standalone UI, configure Harvester to load the UI from an external source.
+
+- Examples of `ui-index`:
+  - Main branch → `https://releases.rancher.com/harvester-ui/dashboard/latest/index.html`
+  - Release series `1.5.x` → `https://releases.rancher.com/harvester-ui/dashboard/release-harvester-v1.5/index.html`
+
+**Steps:**
+1. Go to **Harvester UI** → **Advanced** → **Settings** → **UI**
+2. Set **ui-source** to `External`
+3. Set **ui-index** to the desired URL
+
 ## Contributing
 
-For developers, after reading through the introduction on this page, head over to our [Getting Started](https://extensions.rancher.io/extensions/next/extensions-getting-started) guide to learn more.
+If you want to contribute, start by reading this document, then visit our [Getting Started guide](https://extensions.rancher.io/extensions/next/extensions-getting-started) to learn how to develop and submit changes.
+
+## License
 
-License
-=======
 Copyright (c) 2014-2025 [SUSE, LLC.](https://www.suse.com/)
 
 Licensed under the Apache License, Version 2.0 (the "License");