terraform/docs: link to modules and give an overview what each one does

terraform/README.md

@@ -1,6 +1,16 @@
-# List of terraform modules
+# nixos-anywhere terraform modules
 
-- [all-in-one](all-in-one.md)
-- [install](install.md)
-- [nix-build](nix-build.md)
-- [nixos-rebuild](nixos-rebuild.md)
+These terraform module can run nixos-anywhere from terraform to install nixos as
+well as deploying nixos afterwards.
+
+See what each module does with examples by clicking on the terraform module in
+the following links below:
+
+- [all-in-one](all-in-one.md): Combines the install and nixos-rebuild module in
+  one interface to install NixOS with nixos-anywhere and than keep it up-to-date
+  with nixos-rebuild.
+- [install](install.md): Install NixOS with nixos-anywhere
+- [nixos-rebuild](nixos-rebuild.md): Update NixOS machine with nixos-rebuild on
+  a remote machine
+- [nix-build](nix-build.md): Small helper module to run do build a flake
+  attribute or attribute from a nix file.

terraform/all-in-one.md

@@ -1,5 +1,8 @@
 # All-in-one
 
+Combines the install and nixos-rebuild module in one interface to install NixOS
+with nixos-anywhere and than keep it up-to-date with nixos-rebuild.
+
 ## Example
 
 ```hcl

terraform/install.md

@@ -1,5 +1,7 @@
 # Install
 
+Install NixOS with nixos-anywhere
+
 ## Example
 
 ```hcl

terraform/nix-build.md

@@ -1,5 +1,8 @@
 # Nix-build
 
+Small helper module to run do build a flake attribute or attribute from a nix
+file.
+
 ## Example
 
 - See [install](install.md) or [nixos-rebuild](nixos-rebuild.md)

terraform/nixos-rebuild.md

@@ -1,5 +1,7 @@
 # Nixos-rebuild
 
+Update NixOS machine with nixos-rebuild on a remote machine
+
 ## Example
 
 ```hcl