feat: add Elixir module (#437)

docs/config/README.md

@@ -102,6 +102,7 @@ prompt_order = [
     "hg_branch",
     "package",
     "dotnet",
+    "elixir",
     "elm",
     "golang",
     "haskell",
@@ -470,6 +471,29 @@ variable = "SHELL"
 default = "unknown shell"
 ```
 
+## Elixir
+
+The `elixir` module shows the currently installed version of Elixir and Erlang/OTP.
+The module will be shown if any of the following conditions are met:
+
+- The current directory contains a `mix.exs` file.
+
+### Options
+
+| Variable   | Default      | Description                                            |
+| ---------- | ------------ | ------------------------------------------------------ |
+| `symbol`   | `"💧 "`      | The symbol used before displaying the version of Rust. |
+| `disabled` | `false`      | Disables the `elixir` module.                          |
+
+### Example
+
+```toml
+# ~/.config/starship.toml
+
+[elixir]
+symbol = "🔮 "
+```
+
 ## Git Branch
 
 The `git_branch` module shows the active branch of the repo in your current directory.