nix-shell, nix-env: add page and fix manual link (#5060)

pages/common/nix-env.md

@@ -1,7 +1,7 @@
 # nix-env
 
 > Manipulate or query Nix user environments.
-> More information: <https://nixos.org/releases/nix/latest/manual#sec-nix-env>.
+> More information: <https://nixos.org/manual/nix/stable/#sec-nix-env>.
 
 - List all installed packages:
 

pages/common/nix-shell.md

@@ -0,0 +1,28 @@
+# nix-shell
+
+> Start an interactive shell based on a Nix expression.
+> More information: <https://nixos.org/manual/nix/stable/#sec-nix-shell>.
+
+- Start with nix expression in `shell.nix` or `default.nix` in the current directory:
+
+`nix-shell`
+
+- Run shell command in non-interactive shell and exit:
+
+`nix-shell --run "{{command}} {{command_arguments}}"`
+
+- Start with expression in `default.nix` in the current directory:
+
+`nix-shell {{default.nix}}`
+
+- Start with packages loaded from nixpkgs:
+
+`nix-shell --packages {{package_name_1}} {{package_name_2}}`
+
+- Start with packages loaded from specific nixpkgs revision:
+
+`nix-shell --packages {{package_names}} -I nixpkgs={{https://github.com/NixOS/nixpkgs/archive/nixpkgs_revision.tar.gz}}`
+
+- Evaluate rest of file in specific interpreter, for use in `#!-scripts` (see <https://nixos.org/manual/nix/stable/#use-as-a-interpreter>):
+
+`nix-shell -i {{interpreter}} --packages {{package_names}}`