Add a demo

Author: spyl94

example/package.json

@@ -0,0 +1,8 @@
+{
+    "graphql-doctor": {
+        "schema.graphql": {
+          "ref": "heads/master",
+          "schemaPath": "schema.graphql"
+        }
+    }
+}

example/schema.graphql

@@ -0,0 +1,34 @@
+type Author {
+    id: Int!
+    firstName: String
+    lastName: String
+    """
+    the list of Posts by this author
+    """
+    posts: [Post]
+  }
+
+  enum UserRole {
+    ROLE_ADMIN
+    ROLE_USER
+  }
+
+  type Post {
+    id: Int!
+    title: String
+    author: Author
+    votes: Int
+  }
+
+  # the schema allows the following query:
+  type Query {
+    posts: [Post]
+    author(id: Int! = 1): Author
+  }
+
+  # this schema allows the following mutation:
+  type Mutation {
+    upvotePost (
+      postId: Int
+    ): Post
+  }