Examples folder refactor

🛠 Proposed Refactor

Hi, I am a beginner of PyG, and I get myself familiar with PyG through the documentation, now I want to try to run some examples, I felt a little confused on the current example folder in the repo. The following are my current thoughts, I put it here for your reference, looking forward to hear your feedback.

1. Is it possible to refactor the examples folder, now there are too many separate python scripts in the first level of the example folder, which is not helpful for beginner to get familiar with it, could you please help to tidy it?
2. There are some official tutorial examples in documentation website, it looks quite helpful for beginners, could you also create a notebook folder, and put these notebooks into it?

Suggest a potential alternative/fix

1. Classify the python scripts into several folders according to model or datasets, and provide a better readme file under example folder.
2. Create a notebook folder, and put the colab notebooks code into it.