Apply suggestions from code review

Author: jhansson-ard

content/hardware/09.kits/maker/starter-kit-r4/product.md

@@ -1,7 +1,7 @@
 ---
 title: Starter Kit R4
 url_shop: https://store.arduino.cc/products/starter-kit-r4
-url_guide: https://courses.arduino.cc/starterkitr4
+url_guide: https://courses.arduino.cc/starter-kit-r4/
 primary_button_url: https://courses.arduino.cc/starterkitr4
 primary_button_title: Go To Course
 sku: [K000007_R4, K000007_R4-6P]