doc: add installation example

lib/argon2_elixir.ex

@@ -4,6 +4,29 @@ defmodule Argon2 do
 
   This module provides a secure way to hash passwords using the Argon2i algorithm.
 
+  ## Installation
+
+  Add `argon2` to your list of dependencies in `mix.exs`:
+
+  ```
+  def deps do
+    [
+      {:argon2id_elixir, "~> 1.1.1"}
+    ]
+  end
+  ```
+
+  Ensure you have Rust installed, as it's required for compilation:
+
+  ```sh
+  # On Windows
+  winget install Rust.Rust
+
+  # On Unix-like systems (https://rustup.rs/)
+  curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
+  ```
+
+
   ## Security Presets
 
   * `:owasp` (default) - OWASP recommended settings (m=19456, t=2, p=1)