Update flake.nix to install dependencies automatically

Co-authored-by: pinage404 <pinage404@gmail.com>

Author: y0usaf

flake.nix

@@ -69,7 +69,8 @@
 
         shellHook = ''
           echo "Handy development environment"
-          echo "Run 'bun install' then 'bun run tauri dev' to start"
+          bun install
+          echo "Run 'bun run tauri dev' to start"
         '';
       };
     });