Enhance README with detailed tool description and usage

Expanded the README to provide a detailed overview of the Extension Source Viewer, including features, usage instructions, and notes on reporting issues.

Signed-off-by: Unbounded <ngde@web.de>

Author: UnboundedHQ

README.md

@@ -1,5 +1,39 @@
 # Extension Source Viewer
 
-With modcore Extension Manager, you can download CRX files from other extensions in the Chrome Web Store and upload them here to view the extension's source code and media.
+**Extension Source Viewer** is a web-based tool for examining the source code of Chrome extensions. By uploading a `.crx` file, you can view its extracted contents directly in your browser. All processing takes place locally on your device; no data is transmitted to any server.
 
-Use this tool appropriately.
+This tool is part of the **modcore** ecosystem and is optimized for use with the **modcore Extension Manager**, which provides the “Get CRX of this extension” feature for downloading CRX files from the Chrome Web Store.
+
+---
+
+## Features
+
+- Web-based tool; no installation required  
+- Fully client-side processing for improved privacy and security  
+- Compatible with CRX files downloaded using the modcore Extension Manager  
+- Clear and efficient interface for exploring extension contents
+
+---
+
+## How It Works
+
+1. Install the **modcore Extension Manager** and pin it to the Chrome extensions toolbar.  
+2. Visit any extension page in the Chrome Web Store.  
+3. Right-click the modcore Extension Manager icon and select **“Get CRX of this extension.”**  
+4. After the CRX file is downloaded, open the Extension Source Viewer at:  
+   `https://modcoretech.github.io/extension-source-viewer/viewer.html`  
+5. Upload the CRX file to view and explore the source code.
+
+---
+
+## Notes
+
+- The “Get CRX of this extension” feature works only on the Chrome Web Store.  
+- Some extensions may include protected or obfuscated source code. Such code should not be modified.  
+- Extension Source Viewer is under active development, and improvements are ongoing.
+
+---
+
+## Reporting Issues
+
+If you encounter any problems, please report them in the GitHub issue tracker. Thank you.