[Example] Add Pytorch Geometric Example

.gitignore

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 .Python
 ide_layouts/
 build/
+_build/
 develop-eggs/
 dist/
 downloads/

docs/source/index.rst

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    :name: Examples
    :caption: Examples
 
+   pytorch_ecoystem
    community_examples
    Autoencoder <https://pytorch-lightning-bolts.readthedocs.io/en/latest/autoencoders.html#autoencoders>
    BYOL <https://pytorch-lightning-bolts.readthedocs.io/en/latest/self_supervised_models.html#byol>

docs/source/pytorch_ecoystem.rst

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+Pytorch Ecosystem Examples
+==========================
+
+- `Pytorch Geometric: Deep learning on Graphs and other irregular structures <https://github.com/PyTorchLightning/pytorch-lightning/tree/master/pl_examples/pytorch_ecosystem/pytorch_geometric/README.md>`_.

pl_examples/pytorch_ecosystem/pytorch_geometric/README.md

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+#  [Pytorch Geometric](https://github.com/rusty1s/pytorch_geometric) examples with Lighting
+
+### Introduction
+
+PyTorch Geometric (PyG) is a geometric deep learning extension library for PyTorch. It relies on lower level libraries such as
+
+* PyTorch Cluster: A package consists of a small extension library of highly optimized graph cluster algorithms in Pytorch
+* PyTorch Sparse: A package consists of a small extension library of optimized sparse matrix operations with autograd support in Pytorch
+* PyTorch Scatter: A package consists of a small extension library of highly optimized sparse update (scatter and segment) operations for the use in PyTorch
+
+## Setup
+
+```
+pyenv install 3.7.8
+pyenv local 3.7.8
+python -m venv
+source .venv/bin/activate
+poetry install
+```
+
+Run example
+
+```
+python cora_dna.py
+```
+
+## Current example lists
+
+| `DATASET` | `MODEL` | `TASK` | DATASET DESCRIPTION | MODEL DESCRIPTION                                                                                                                                                                   |                                                                                                                                                                     |
+| ------------- | ----------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ---------------------------- | --- |
+| Cora          | DNA          | Node Classification | The citation network datasets "Cora", "CiteSeer" and "PubMed" from the "Revisiting Semi-Supervised Learning with Graph Embeddings" <https://arxiv.org/abs/1603.08861> | The dynamic neighborhood aggregation operator from the "Just Jump: Towards Dynamic Neighborhood Aggregation in Graph Neural Networks"
+
+
+## DATASET SIZES
+
+```
+ 16M    ./cora
+```