Add entries to get started toc

Author: karenzone

get-started/toc.yml

@@ -2,6 +2,10 @@ project: 'Get started'
 toc:
   - file: index.md
   - file: the-stack.md
+    children:
+      - file: stack-components.md
+      - file: introduction.md
+      - file: installing-elastic-stack.md
   - file: deployment-options.md
   - file: use-cases.md
   - file: contribute.md