add better documentation around query param usage (#42)

Author: jbonzo

README.md

@@ -63,6 +63,44 @@ if __name__ == '__main__':
 
 ```
 
+### Query parameters for REST calls
+
+Every function call under our RESTClient has the `query_params` kwargs. These kwargs are passed along and mapped 1:1
+as query parameters to the underling HTTP call. For more information on the different query parameters please reference
+our [API Docs](https://polygon.io/docs/).
+
+#### Example with query parameters
+
+```python
+import datetime
+
+from polygon import RESTClient
+
+
+def ts_to_datetime(ts) -> str:
+    return datetime.datetime.fromtimestamp(ts / 1000.0).strftime('%Y-%m-%d %H:%M')
+
+
+def main():
+    key = "your api key"
+
+    # RESTClient can be used as a context manager to facilitate closing the underlying http session
+    # https://requests.readthedocs.io/en/master/user/advanced/#session-objects
+    with RESTClient(key) as client:
+        from_ = "2019-01-01"
+        to = "2019-02-01"
+        resp = client.stocks_equities_aggregates("AAPL", 1, "minute", from_, to, unadjusted=False)
+
+        print(f"Minute aggregates for {resp.ticker} between {from_} and {to}.")
+
+        for result in resp.results:
+            dt = ts_to_datetime(result["t"])
+            print(f"{dt}\n\tO: {result['o']}\n\tH: {result['h']}\n\tL: {result['l']}\n\tC: {result['c']} ")
+
+
+if __name__ == '__main__':
+    main()
+```  
 
 ## Notes about the REST Client