website/docs: add icon info to style guide (#18832)

website/docs/developer-docs/docs/style-guide.mdx

@@ -394,6 +394,8 @@ When documenting errors, follow this structure:
 - **Diagrams**:
     - Use [Mermaid](https://mermaid.js.org/) for creating diagrams directly in markdown. Mermaid is our preferred tool for documentation diagrams as it allows for version control and easy updates.
     - For more complex diagrams, you can use tools like [Draw.io](https://draw.io). Ensure high contrast and text descriptions.
+- **authentik icons**:
+    - For authentik icons in integration guides, reference assets from the user's own self-hosted instance to avoid external calls, for example: `https://authentik.company/static/dist/assets/icons/icon.svg`
 
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