add GitHub link (#63)

Author: dannysheridan

fern/docs.yml

@@ -21,12 +21,14 @@ navigation:
   - api: API Reference
 
 navbar-links:
-  - type: secondary
+  - type: minimal
     text: Fork this repo
     url: https://github.com/fern-api/docs-starter
-  - type: primary
+  - type: filled
     text: Get a demo
     url: https://buildwithfern.com/contact?utm_campaign=demo&utm_medium=plantstore&utm_source=navbar
+  - type: github
+    value: https://github.com/fern-api/fern
 
 colors:
   accentPrimary: