add example readme

examples/README.md

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+Example files for HIPPYNN 
+-------------------------
+
+The files in this directory provide examples for hippynn.
+Because hippynn is for training and running machine learning models,
+it requires data to run! Our example files typically contain
+a header which describes where to get the data in order to run the example.
+Occasionally an example file for running a model depends on running a
+different example for training that model.
+
+
+Suggested Starting Points
+-------------------------
+
+- If you're looking to get a basic picture of how hippynn works, see
+``barebones.py``, which is about as simple of an example as can function.
+If you have a basic understanding but want to see more details,
+check out the jupyter notebooks ``graph_exploration.ipynb``.
+
+- If you're looking to customize a nicely constructed training script,
+ look into ``ani1x_training.py``. This trains to a large dataset
+ known as ani1x, and separates out the various aspects of the 
+ library as well as demonstrating how they interact together.
+ It has many optional features included. 
+
+- If you want to see how to use a model with ase or lammps,
+first train a model with ``ani_aluminum_example.py``. 
+Then check out ``ase_example.py`` or the ``examples/lammps/``
+directory respectively.