Fixing missing files (#678)

* fix links

* missing import lamb

* reorder

Author: autoih

docs/overview.md

@@ -126,9 +126,9 @@ warning.
 
 ## Contributing
 TF-Addons is a community led open source project. As such, the project
-depends on public contributions, bug-fixes, and documentation. Please
-see [contribution guidelines](CONTRIBUTING.md) for a guide on how to
-contribute. This project adheres to [TensorFlow's code of conduct](CODE_OF_CONDUCT.md).
+depends on public contributions, bug-fixes, and documentation. Please see 
+[contribution guidelines](https://github.com/tensorflow/addons/blob/master/CONTRIBUTING.md) 
+for a guide on how to contribute. This project adheres to [TensorFlow's code of conduct](https://github.com/tensorflow/addons/blob/master/CODE_OF_CONDUCT.md).
 By participating, you are expected to uphold this code.
 
 ## Community

tensorflow_addons/optimizers/__init__.py

@@ -19,6 +19,7 @@
 from __future__ import print_function
 
 from tensorflow_addons.optimizers.conditional_gradient import ConditionalGradient
+from tensorflow_addons.optimizers.lamb import LAMB
 from tensorflow_addons.optimizers.lazy_adam import LazyAdam
 from tensorflow_addons.optimizers.lookahead import Lookahead
 from tensorflow_addons.optimizers.moving_average import MovingAverage