docs(readme): add demo section with video link to showcase CmdBook functionality

Author: doniaskima

README.md

@@ -6,7 +6,9 @@
 CmdBook is a small CLI for storing and retrieving shell commands.  
 It keeps a local SQLite database with an FTS5 index for fast search. It does **not** execute commands; it helps you remember, organize, and copy/paste them quickly.
 
----
+## Demo
+
+## ▶️ [Watch CmdBook in action](record/record.mov)
 
 ## Features