add terraform section in documentation

docs/SUMMARY.md

@@ -19,5 +19,6 @@ Refer to the following documentation for more information.
 - [Using your own kexec image](./howtos/custom-kexec.md)
 - [Secrets and full disk encryption](./howtos/secrets.md)
 - [Use without flakes](./howtos/use-without-flakes.md)
+- [Terraform](./howtos/terraform.md)
 
 [Reference](./reference.md): Reference Guide

docs/howtos/INDEX.md

@@ -15,3 +15,5 @@
 [Secrets and full disk encryption](./secrets.md)
 
 [Use without flakes](./use-without-flakes.md)
+
+[Terraform](./terraform.md)

docs/howtos/terraform.md

@@ -0,0 +1,23 @@
+# Terraform
+
+The nixos-anywhere terraform modules allow you to use Terraform for installing
+and updating NixOS. It simplifies the deployment process by integrating
+nixos-anywhere functionality.
+
+Our terraform module requires the
+[null](https://registry.terraform.io/providers/hashicorp/null/latest) and
+[external](https://registry.terraform.io/providers/hashicorp/external/latest)
+provider.
+
+You can get these by from nixpkgs like this:
+
+```nix
+nix-shell -p '(pkgs.terraform.withPlugins (p: [ p.null p.external ]))'
+```
+
+You can add this expression the `packages` list in your devshell in flake.nix or
+in shell.nix.
+
+Checkout out the
+[module reference](https://github.com/numtide/nixos-anywhere/tree/main/terraform)
+for examples and module parameter on how to use the modules.