Update docs

Author: lululxvi

README.md

@@ -56,7 +56,7 @@ All the components of DeepXDE are loosely coupled, and thus DeepXDE is well-stru
 
 DeepXDE requires [TensorFlow](https://www.tensorflow.org/) to be installed. Both TensorFlow 1 and TensorFlow 2 can be used as the DeepXDE backend, but TensorFlow 1 is recommended, because in my tests TensorFlow 2 is 2x~3x slower than TensorFlow 1.
 
-Then, you can install DeepXDE itself. If you use TensorFlow 2, you need to install DeepXDE by cloning the folder. If you use Python 2, you need to install DeepXDE using `pip`.
+Then, you can install DeepXDE itself. If you use Python 2, you need to install DeepXDE using `pip`.
 
 - Install the stable version with `pip`:
 

docs/modules/deepxde.rst

@@ -61,6 +61,14 @@ deepxde.display module
     :undoc-members:
     :show-inheritance:
 
+deepxde.external\_optimizer module
+----------------------------------
+
+.. automodule:: deepxde.external_optimizer
+    :members:
+    :undoc-members:
+    :show-inheritance:
+
 deepxde.fractional module
 -------------------------
 

docs/user/installation.rst

@@ -3,7 +3,7 @@ Installation
 
 DeepXDE requires `TensorFlow <https://www.tensorflow.org/>`_ to be installed. Both TensorFlow 1 and TensorFlow 2 can be used as the DeepXDE backend, but TensorFlow 1 is recommended, because in my tests TensorFlow 2 is 2x~3x slower than TensorFlow 1.
 
-Then, you can install DeepXDE itself. If you use TensorFlow 2, you need to install DeepXDE by cloning the folder.  If you use Python 2, you need to install DeepXDE using ``pip``.
+Then, you can install DeepXDE itself. If you use Python 2, you need to install DeepXDE using ``pip``.
 
 - Install the stable version with ``pip``::