adding a demo gif

Author: ashishkurmi

README.md

@@ -4,6 +4,10 @@
   <img src="images/banner.png" alt="StepSecurity Dev Machine Guard — shield logo with terminal prompt" width="800">
 </p>
 
+<p align="center">
+  <img src="images/demo.gif" alt="StepSecurity Dev Machine Guard demo" width="800">
+</p>
+
 <p align="center">
   <a href="https://github.com/step-security/dev-machine-guard/actions/workflows/shellcheck.yml"><img src="https://github.com/step-security/dev-machine-guard/actions/workflows/shellcheck.yml/badge.svg" alt="ShellCheck CI"></a>
   <a href="LICENSE"><img src="https://img.shields.io/badge/license-Apache%202.0-blue.svg" alt="License: Apache 2.0"></a>