Update README and add screenshot

CONTRIBUTING.md

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-
 # Contributing
 
 This project welcomes contributions and suggestions.  Most contributions require you to agree to a

README.md

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-# Mezzurite-DevTools
+# Mezzurite Developer Tools
 
-This extension helps developers verify their web application's onboarding onto Mezzurite.
+Mezzurite Developer Tools allow you to view Mezzurite metrics for any application being instrumented with [Mezzurite](https://github.com/Microsoft/Mezzurite "Mezzurite").
+
+<center>
+  <img src="res/img/devtools-screenshot.png" alt="Dev tools screenshot" height="40%" width="40%">
+</center>
+
+## Requirements
+You need an [Angular](https://github.com/Microsoft/Mezzurite/blob/master/Mezzurite.Angular/README.md "Angular"), [AngularJS](https://github.com/Microsoft/Mezzurite/blob/master/Mezzurite.AngularJS/README.md "AngularJS"), or [React](https://github.com/Microsoft/Mezzurite/blob/master/Mezzurite.React/README.md "React") application running Mezzurite.
+
+## Installation
+To install, download the latest [release](https://github.com/Microsoft/Mezzurite-DevTools/releases "release"), or clone the repository and build the extension by running `npm run build`.
+
+Navigate to [chrome://extensions](chrome://extensions "chrome://extensions") and select `Load unpacked`, selecting the `/dist` folder output from the build.
 
 ## Contributions
-[To read about contributing to this repo, click here](CONTRIBUTING.md)
+[To read about contributing to this repo, click here](CONTRIBUTING.md)