Add notebook links for ddim inversion

Author: johnowhitaker

unit4/README.md

@@ -153,6 +153,7 @@ Key references
 
 | Chapter                                     | Colab                                                                                                                                                                                               | Kaggle                                                                                                                                                                                                   | Gradient                                                                                                                                                                               | Studio Lab                                                                                                                                                                                                   |
 |:--------------------------------------------|:----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|:---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|:---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|:-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| DDIM Inversion                                | [![Open In Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/huggingface/diffusion-models-class/blob/main/unit4/01_ddim_inversion.ipynb)              | [![Kaggle](https://kaggle.com/static/images/open-in-kaggle.svg)](https://kaggle.com/kernels/welcome?src=https://github.com/huggingface/diffusion-models-class/blob/main/unit4/01_ddim_inversion.ipynb)              | [![Gradient](https://assets.paperspace.io/img/gradient-badge.svg)](https://console.paperspace.com/github/huggingface/diffusion-models-class/blob/main/unit4/01_ddim_inversion.ipynb)              | [![Open In SageMaker Studio Lab](https://studiolab.sagemaker.aws/studiolab.svg)](https://studiolab.sagemaker.aws/import/github/huggingface/diffusion-models-class/blob/main/unit4/01_ddim_inversion.ipynb)              |
 | Diffusion for Audio                                | [![Open In Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/huggingface/diffusion-models-class/blob/main/unit4/02_diffusion_for_audio.ipynb)              | [![Kaggle](https://kaggle.com/static/images/open-in-kaggle.svg)](https://kaggle.com/kernels/welcome?src=https://github.com/huggingface/diffusion-models-class/blob/main/unit4/02_diffusion_for_audio.ipynb)              | [![Gradient](https://assets.paperspace.io/img/gradient-badge.svg)](https://console.paperspace.com/github/huggingface/diffusion-models-class/blob/main/unit4/02_diffusion_for_audio.ipynb)              | [![Open In SageMaker Studio Lab](https://studiolab.sagemaker.aws/studiolab.svg)](https://studiolab.sagemaker.aws/import/github/huggingface/diffusion-models-class/blob/main/unit4/02_diffusion_for_audio.ipynb)              |
 
 We've covered a LOT of different ideas in this unit, many of which deserve much more detailed follow-on lessons in the future. For now, you can two of the many topics via the hands-on notebooks we've prepared.