Update UPGRADE-v2.0.md

Migration docs improvement

UPGRADE-v2.0.md

@@ -122,6 +122,13 @@ def resolve_my_field(self, info, my_arg):
     return ...
 ```
 
+**PS.: Take care with receiving args like `my_arg` as above. This doesn't work for optional (non-required) arguments as stantard `Connection`'s arguments (first, before, after, before).**
+You may need something like this:
+
+```python
+def resolve_my_field(self, info, known_field1, known_field2, **args): ## get other args with: args.get('arg_key')
+```
+
 And, if you need the context in the resolver, you can use `info.context`:
 
 ```python
@@ -193,7 +200,42 @@ class MyObject(ObjectType):
 
 ## Mutation.mutate
 
-Now only receives (`root`, `info`, `**args`)
+Now only receives (`self`, `info`, `**args`) and if not a @classmethod
+
+Before:
+
+```python
+class SomeMutation(Mutation):
+    ...
+    
+    @classmethod
+    def mutate(cls, instance, args, context, info):
+        ...
+```
+
+With 2.0:
+
+```python
+class SomeMutation(Mutation):
+    ...
+    
+    def mutate(self, info, **args):
+        ...
+```
+
+With 2.0 you can also get your declared (as above) `args` this way:
+
+```python
+class SomeMutation(Mutation):
+    class Arguments:
+        first_name = String(required=True)
+        last_name = String(required=True)
+    ...
+    
+    def mutate(self, info, first_name, last_name):
+        ...
+```
+
 
 
 ## ClientIDMutation.mutate_and_get_payload
@@ -201,6 +243,35 @@ Now only receives (`root`, `info`, `**args`)
 Now only receives (`root`, `info`, `**input`)
 
 
+### Middlewares
+
+If you are using Middelwares, you need to some adjustments:
+
+Before:
+
+```python
+class MyGrapheneMiddleware(object):    
+    def resolve(self, next_mw, root, args, context, info):
+
+        ## Middleware code
+
+        return next_mw(root, args, context, info)
+```
+
+With 2.0:
+
+```python
+class MyGrapheneMiddleware(object):    
+    def resolve(self, next_mw, root, info, **args):
+        context = info.context
+
+        ## Middleware code
+
+        info.context = context
+        return next_mw(root, info, **args)```
+```
+
+
 ## New Features
 
 ### InputObjectType