Add Colab badges for the new deep-dive notebooks to README

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: iLampard

README.md

@@ -114,6 +114,8 @@ Explore the following tutorials that can be opened directly in Google Colab:
 - [![Open in Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/ant-research/EasyTemporalPointProcess/blob/main/notebooks/easytpp_1_dataset.ipynb) Tutorial 1: Dataset in EasyTPP.
 - [![Open in Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/ant-research/EasyTemporalPointProcess/blob/main/notebooks/easytpp_2_tfb_wb.ipynb) Tutorial 2: Tensorboard in EasyTPP.
 - [![Open in Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/ant-research/EasyTemporalPointProcess/blob/main/notebooks/easytpp_3_train_eval.ipynb) Tutorial 3: Training and Evaluation of TPPs.
+- [![Open in Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/ant-research/EasyTemporalPointProcess/blob/main/notebooks/easytpp_intensityfree_log_stats.ipynb) Deep dive: log-space statistics in IntensityFree (issue [#84](https://github.com/ant-research/EasyTemporalPointProcess/issues/84)).
+- [![Open in Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/ant-research/EasyTemporalPointProcess/blob/main/notebooks/easytpp_multistep_generation.ipynb) Deep dive: multi-step event generation and intensity-free thinning (issue [#13](https://github.com/ant-research/EasyTemporalPointProcess/issues/13)).
 
 ### End-to-end Example