adding shun's github handle to callback maintainers list (#918)

* adding shun's github handle to callback maintainers list

* update CODEOWNERS

Author: shun-lin

.github/CODEOWNERS

@@ -5,7 +5,7 @@
 
 # Subpackage Owners
 /tensorflow_addons/activations/ @facaiy @seanpmorgan
-/tensorflow_addons/callbacks/ @squadrick
+/tensorflow_addons/callbacks/ @squadrick @shun-lin
 /tensorflow_addons/image/ @windqaq @facaiy 
 /tensorflow_addons/layers/ @seanpmorgan @facaiy
 /tensorflow_addons/losses/ @facaiy @windqaq

README.md

@@ -30,7 +30,7 @@ developments that cannot be integrated into core TensorFlow
 | Subpackage    | Maintainers  | Contact Info                        |
 |:----------------------- |:----------- |:----------------------------|
 | [tfa.activations](tensorflow_addons/activations/README.md) | SIG-Addons | @facaiy @seanpmorgan | 
-| [tfa.callbacks](tensorflow_addons/callbacks/README.md) | SIG-Addons | @squadrick |
+| [tfa.callbacks](tensorflow_addons/callbacks/README.md) | SIG-Addons | @squadrick @shun-lin |
 | [tfa.image](tensorflow_addons/image/README.md) | SIG-Addons | @windqaq @facaiy |
 | [tfa.layers](tensorflow_addons/layers/README.md) | SIG-Addons | @seanpmorgan @facaiy |
 | [tfa.losses](tensorflow_addons/losses/README.md) | SIG-Addons | @facaiy @windqaq   |