Add ScalarDB GraphQL and SQL overview pages

Author: josh-wong

versioned_sidebars/version-3.12-sidebars.json

@@ -370,6 +370,11 @@
               "label": "SQL Interface",
               "collapsible": true,
               "items": [
+                {
+                  "type": "doc",
+                  "id": "scalardb-sql/index",
+                  "label": "Overview"
+                },
                 {
                   "type": "doc",
                   "id": "scalardb-sql/jdbc-guide",
@@ -402,6 +407,11 @@
               "label": "GraphQL Interface",
               "collapsible": true,
               "items": [
+                {
+                  "type": "doc",
+                  "id": "scalardb-graphql/index",
+                  "label": "Overview"
+                },
                 {
                   "type": "doc",
                   "id": "scalardb-graphql/how-to-run-two-phase-commit-transaction",