Document update-types feature within the allow block (#5582)

Author: yeikel

src/schemas/json/dependabot-2.0.json

@@ -744,6 +744,10 @@
               },
               "dependency-type": {
                 "$ref": "#/definitions/dependency-type"
+              },
+              "update-types": {
+                "$ref": "#/definitions/update-types",
+                "description": "Use to allow specific types of updates. You can combine this with 'dependency-name: \"*\"' to allow particular update-types for all dependencies."
               }
             },
             "anyOf": [