docs(sage): Add how to run

notebook/sagemath/flake.nix

@@ -1,5 +1,15 @@
 {
-  description = "Sagemath flake";
+  description = ''
+    Sagemath flake
+
+    You'll want to run the flake with the following command:
+
+    $ sage --nodotsage -n=jupyterlab --notebook-dir /path/to/notebooks
+
+    For example:
+
+    $ sage --nodotsage -n=jupyterlab --notebook-dir .
+  '';
 
   inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
   inputs.flake-utils.url = "github:numtide/flake-utils";
@@ -14,12 +24,8 @@
       in {
         devShells.default = pkgs.mkShell {
           buildInputs = with pkgs; [
-            sage
+            sageWithDoc
           ];
-
-          shellHook = ''
-            sage --nodotsage -n=jupyterlab --notebook-dir .
-          '';
         };
       }
     );