Add description and video to README file

README.md

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 # Supply Chain Security Java
 
+Samples showing how to secure the supply chain for Java applications, including:
+
+* SBOMs with CycloneDX and SPDX
+* Dependency Management with Gradle and Maven
+* Cryptographic signatures, policies, and SLSA
+
+## Pre-requisites
+
+* Java 21
+
+## Devoxx Belgium 2023
+
+[![Watch the video](https://img.youtube.com/vi/ftPFxK8JPNM/hqdefault.jpg)](https://www.youtube.com/embed/ftPFxK8JPNM)
+
 Software supply chain security has never been more critical, and protecting our systems from bad actors and vulnerabilities is a constant challenge.
 
 Do you know whether your Git commits are being manipulated without your knowledge? Are you confident that you have complete visibility of all the libraries and dependencies in your application JARs and container images? Can you trust the results of your vulnerability scanner? And how can you verify the integrity of your applications in production?