added graphene import to READMEs (#1183)

it's nice to just be able to copy/paste the entire example without
having to remember the import

Author: kimbo

README.md

@@ -45,6 +45,8 @@ pip install "graphene>=2.0"
 Here is one example for you to get started:
 
 ```python
+import graphene
+
 class Query(graphene.ObjectType):
     hello = graphene.String(description='A typical hello world')
 

README.rst

@@ -67,6 +67,8 @@ Here is one example for you to get started:
 
 .. code:: python
 
+    import graphene
+
     class Query(graphene.ObjectType):
         hello = graphene.String(description='A typical hello world')