dependencies for sphinx (#87)

README.md

@@ -18,7 +18,11 @@ After installing the correct PyTorch, all you need is clone the repository and d
 pip install .
 ```
 
-After TorchANI has been installed, you can build the documents by running `sphinx-build docs build`.
+After TorchANI has been installed, you can build the documents by running `sphinx-build docs build`. But make sure you
+install dependencies:
+```bash
+pip install sphinx sphinx-gallery pillow matplotlib sphinx_rtd_theme
+```
 
 # Paper
 
@@ -36,4 +40,4 @@ You must pass all the tests on GitHub before your PR can be merged.
 
 Code review is required before merging pull request.
 
-To manually run unit tests, do `python setup.py test`
+To manually run unit tests, do `python setup.py test`
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