feat(cli): documented optional supertypes Array<string> in grammar-schema.json

cli/src/generate/grammar-schema.json

@@ -1,4 +1,6 @@
 {
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "title": "tree-sitter grammar specification",
   "type": "object",
 
   "required": ["name", "rules"],
@@ -7,6 +9,7 @@
 
   "properties": {
     "name": {
+      "description": "the name of the grammar",
       "type": "string",
       "pattern": "^[a-zA-Z_]\\w*"
     },
@@ -57,6 +60,15 @@
     "word": {
       "type": "string",
       "pattern": "^[a-zA-Z_]\\w*"
+    },
+
+    "supertypes": {
+      "description": "each supertype instructs the parser to replace a set of subtypes in the `types` list with a single supertype.",
+      "type": "array",
+      "items": {
+        "description": "the name of a rule in `rules` or `extras`",
+        "type": "string"
+      }
     }
   },