Mention fonts installation

Author: dannyadair

README.md

@@ -31,10 +31,17 @@ pipx ensurepath
   ```
 
 - For PDF compression, install [Ghostscript](https://www.ghostscript.com/):
+
   ```bash
   sudo apt install ghostscript
   ```
 
+- If you want to embed particular fonts, they need to be installed. For example for
+  [Roboto fonts](https://fonts.google.com/specimen/Roboto):
+  ```bash
+  sudo apt install fonts-roboto
+  ```
+
 ### Basic Usage
 
 1. Create your document design in an SVG editor