Updated v3 release notes (markdown)

v3-release-notes.md

@@ -14,7 +14,54 @@ Graphene builds on top of the excellent [GraphQL-core](https://github.com/graphq
 
 ### Better Enum support
 
-TODO
+Graphene v3 introduces better Enum support which should improve the developer experience of working with them in Graphene. Previously when resolving an Enum you had to return the Enum value from the field resolver. In v3 you can now return the Enum member directly:
+
+```python
+from graphene import Enum, ObjectType, Schema
+
+class Color(Enum):
+    RED = 1
+    GREEN = 2
+    BLUE = 3
+
+class Query(ObjectType):
+    color = Color(required=True)
+
+    def resolve_color(root, info):
+        return Color.RED
+
+schema = Schema(query=Query)
+result = schema.execute("query { color }")
+assert result.data["color"] == "RED"
+```
+
+(This change is completely backwards compatible so any resolvers that return the member value will still work)
+
+Also when Enum's are used as an input to a field the resolver now receives the Enum member directly rather than the value:
+
+```python
+from graphene import Enum, ObjectType, Schema
+
+class Color(Enum):
+    RED = 1
+    GREEN = 2
+    BLUE = 3
+
+class Query(ObjectType):
+    color = Color(required=True, color_input=Color(required=True))
+
+    def resolve_color(root, info, color_input):
+        assert color_input is Color.RED
+        return color_input
+
+schema = Schema(query=Query)
+result = schema.execute("query { color(colorInput: RED) }")
+assert result.data["color"] == "RED"
+```
+
+⚠️ This is a breaking change. You will need to update any resolvers or mutations that accept enums as inputs to support this change. ⚠️ 
+
+Ref: https://github.com/graphql-python/graphene/pull/1153
 
 ### Fast ObjectType creation
 
@@ -43,4 +90,8 @@ TODO
 
 TODO
 
+---
+
+A huge thanks to everyone involved in bringing this release together!
+
 Full changelog https://github.com/graphql-python/graphene/compare/v2.1.8...v3.0.0