Update index.md

Author: Bangkah

content/rest/guides/index.md

@@ -21,6 +21,7 @@ children:
   - /using-the-rest-api-to-interact-with-your-git-database
   - /using-the-rest-api-to-interact-with-checks
   - /encrypting-secrets-for-the-rest-api
+  - /rest-api-quickstart
 ---
 This section of the documentation is intended to get you up-and-running with
 real-world {% data variables.product.github %} API applications. We'll go over everything you need to know, from authentication to results manipulation to integrating results with other apps.