Add example for using base resource

examples/base_resource.py

@@ -0,0 +1,18 @@
+import os
+
+from sparkpost.base import Resource
+
+
+class Webhooks(Resource):
+    key = "webhooks"
+
+    def list(self, **kwargs):
+        results = self.request('GET', self.uri, **kwargs)
+        return results
+
+
+api_key = os.environ.get('SPARKPOST_API_KEY', None)
+webhooks = Webhooks('https://api.sparkpost.com/api/v1', api_key)
+
+# returns a list of webhooks for your account
+print(webhooks.list())