Add missing toplevel "jsx" to build schema.

See #5646

Author: cristianoc

docs/docson/build-schema.json

@@ -438,6 +438,10 @@
       "type": "boolean",
       "description": "Ignore generators, cut the dependency on generator tools"
     },
+    "jsx": {
+      "$ref": "#/definitions/jsx-specs",
+      "description": "Configuration for the JSX transformation."
+    },
     "reason": {
       "$ref": "#/definitions/reason-specs",
       "description": "ReScript comes with [Reason](http://reasonml.github.io/) by default. Specific configurations here."