add basic menu to docs configuration

Author: joonlabs

docs/_config.yml

@@ -1 +1,12 @@
-theme: jekyll-theme-cayman
+theme: jekyll-theme-cayman
+docs:
+  - title: Introduction
+    url: /
+  - title: Getting Started
+    url: getting-started.html
+  - title: Schema Definition
+    url: schema-definition.html
+  - title: Parsing, Validating and Executing
+    url: parsing-validating-executing.html
+  - title: Server
+    url: server.html