add order book example

stock/examples.json

@@ -41,5 +41,36 @@
             "low": 115.83,
             "date": "2020-10-01"
         }
+    }],
+    "orderbook": [{
+        "title": "Order book history",
+        "description": "Returns historic order book for a given date",
+        "request": {
+            "stock": "AAPL",
+            "date": "2020-10-01"
+        },
+        "response": {
+            "symbol": "AAPL",
+            "date": "2020-10-01",
+            "orders": [
+                {
+                    "bid_price": 101,
+                    "bid_size": 112,
+                    "timestamp": "2020-10-01T08:00:00.037685138Z"
+                },
+                {
+                    "bid_price": 116.52,
+                    "bid_size": 1,
+                    "timestamp": "2020-10-01T08:00:00.053150454Z"
+                },
+                {
+                    "ask_price": 116.92,
+                    "bid_price": 116.7,
+                    "ask_size": 1,
+                    "bid_size": 3,
+                    "timestamp": "2020-10-01T08:00:17.417598642Z"
+                }
+           ]
     }]
+
 }