Add intial main.py file

devenv.nix

@@ -6,7 +6,11 @@
     };
   };
 
-  packages = [];
+  packages = [
+    pkgs.python313Packages.click
+    pkgs.python313Packages.ebooklib
+    pkgs.python313Packages.requests
+  ];
 
   git-hooks = {
     enable = true;

main.py

@@ -0,0 +1,7 @@
+def main() -> None:
+    """main function."""
+    pass
+
+
+if __name__ == "__main__":
+    main()