Add "Startup sequence" sub-page to ENSIndexer docs (#2012)

Co-authored-by: lightwalker.eth <126201998+lightwalker-eth@users.noreply.github.com>

Author: tk-o

.changeset/huge-weeks-dance.md

@@ -0,0 +1,5 @@
+---
+"@docs/ensnode": minor
+---
+
+Added "Startup sequence" page to ENSIndexer docs.

docs/ensnode.io/config/integrations/starlight.ts

@@ -159,6 +159,11 @@ export function starlight(): AstroIntegration {
                 },
               ],
             },
+            {
+              label: "Concepts",
+              collapsed: false,
+              autogenerate: { directory: "ensindexer/concepts" },
+            },
             {
               label: "Using ENSIndexer",
               collapsed: false,