docs: add documentation for file-exists action

Author: FidelusAleksander

README.md

@@ -22,6 +22,8 @@ This repository serves as a comprehensive toolkit for creating and managing GitH
 
 - **[.github/workflows](/.github/workflows)**: GitHub Actions workflows for automating common parts of Skills Exercises
 - **[markdown-templates](/markdown-templates)**: Ready-to-use Markdown templates for creating consistent exercise documentation, instructions, and README files
+- **[actions](/actions)**: Simple composite actions to help when building GitHub Skills exercises
+
 
 ## Examples
 

actions/file-exists/README.md

@@ -0,0 +1,22 @@
+# File Exists :package:
+
+A GitHub Action that checks if a file exists in the repository.
+
+This action will fail if the file does not exist
+
+## Inputs ⚙️
+
+| Name   | Description                                                    | Required |
+| ------ | -------------------------------------------------------------- | -------- |
+| `file` | The path to the file to check, relative to the repository root | Yes      |
+
+## Usage 🚀
+
+```yaml
+steps:
+  - uses: actions/checkout@v4
+  - name: Check if file exists
+    uses: skills/exercise-toolkit/actions/file-exists@<git-tag>
+    with:
+      file: "path/to/your/file.md"
+```