docs: minor usage addition

README.md

@@ -2,10 +2,6 @@
 
 Generate fallback fonts from a CSS file using fontpie.
 
-```bash
-npx fontpie-from-css <css-file>
-```
-
 [build badge]:
 	https://img.shields.io/github/actions/workflow/status/matt-kinton/fontpie-from-css/release.yml?branch=main&logo=github&style=flat-square
 [build]:
@@ -14,6 +10,15 @@ npx fontpie-from-css <css-file>
 	https://img.shields.io/badge/license-MIT%20License-blue.svg?style=flat-square
 [license]: https://github.com/matt-kinton/fontpie-from-css/blob/main/LICENSE
 
+## Usage
+
+```bash
+npx fontpie-from-css <css-file>
+```
+
+**Note:** Font files are loaded relative to the CSS file, ideally the CSS file
+should be in the same directory as the font files.
+
 ## Credit
 
 This project is a simple wrapper around