Add tutorial notebooks with link to run on colab (#234)

Co-authored-by: Josh Robinson <[email protected]>

README.md

@@ -159,10 +159,10 @@ task.evaluate(val_pred, val_table)
 # Tutorials
 To get started with RelBench, we provide some helpful Colab notebook tutorials. These tutorials cover (i) how to load data using RelBench, focusing on providing users with the understanding of RelBench data logic needed to use RelBench data freely with any desired ML models, and (ii) training a GNN predictive model to solve tasks in RelBench. Please refer to the code for more detailed documentation.
 
-| Name | Colab | Description |
-|-------|-------|---------------------------------------------------------|
-| Loading Data | [<img align="center" src="https://colab.research.google.com/assets/colab-badge.svg" />](https://colab.research.google.com/drive/1PAOktBqh_3QzgAKi53F4JbQxoOuBsUBY?usp=sharing) | How to load and explore RelBench data
-| Training models | [<img align="center" src="https://colab.research.google.com/assets/colab-badge.svg" />](https://colab.research.google.com/drive/1_z0aKcs5XndEacX1eob6csDuR4DYhGQU?usp=sharing)| Train your first GNN-based model on RelBench. |
+| Name | Notebook | Try on Colab | Description |
+|-------|----------|--------------|---------------------------------------------------------|
+| Loading Data | [load_data.ipynb](tutorials/load_data.ipynb) | [<img align="center" src="https://colab.research.google.com/assets/colab-badge.svg" />](https://colab.research.google.com/github/snap-stanford/relbench/blob/main/tutorials/load_data.ipynb) | How to load and explore RelBench data
+| Training models | [train_model.ipynb](tutorials/train_model.ipynb) | [<img align="center" src="https://colab.research.google.com/assets/colab-badge.svg" />](https://colab.research.google.com/github/snap-stanford/relbench/blob/main/tutorials/train_model.ipynb)| Train your first GNN-based model on RelBench. |