docs: add the Shannon naming section and swap in the 3.0 demo GIF

- explain the Claude Shannon information-theory origin under "What is Shannon?"
- point "Shannon in Action" at the 3.0 recording in assets/Shannon3GIF.gif

Both taken from the README half of #438.

README.md

@@ -57,10 +57,16 @@ Thanks to tools like Claude Code and Cursor, your team ships code non-stop. But
 
 Shannon closes that gap by providing on-demand, automated penetration testing that can run against every build or release.
 
+### Why "Shannon"?
+
+It's named after Claude Shannon, the father of information theory. At its core, pentesting is an information problem: every probe reduces uncertainty about a system's state. The best tools maximize the signal gained from every request, turning those bits of knowledge into an exploit path.
+
+Also, we wanted you to be able to say, "Hey Claude, run Shannon" to find all the security flaws in your vibe-coded app.
+
 ## Shannon in Action
 
 <p align="center">
-  <img src="assets/shannon-action.gif" alt="Shannon running an autonomous pentest" width="100%">
+  <img src="assets/Shannon3GIF.gif" alt="Shannon running an autonomous pentest" width="100%">
 </p>
 
 Sample penetration test reports from intentionally vulnerable applications, produced by Shannon Open Source: