Add Google Colab badge (#89)

Author: g4brielvs

README.md

@@ -6,6 +6,7 @@
 [![tests](https://github.com/worldbank/blackmarblepy/actions/workflows/tests.yml/badge.svg)](https://github.com/worldbank/blackmarblepy/actions/workflows/tests.yml)
 [![pre-commit.ci status](https://results.pre-commit.ci/badge/github/worldbank/blackmarblepy/main.svg)](https://results.pre-commit.ci/latest/github/worldbank/blackmarblepy/main)
 [![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.10667907.svg)](https://zenodo.org/doi/10.5281/zenodo.10667907)
+[![Open In Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/worldbank/blackmarblepy/blob/main/notebooks/blackmarblepy.ipynb)
 [![Downloads](https://static.pepy.tech/badge/blackmarblepy)](https://pepy.tech/project/blackmarblepy)
 [![GitHub Repo stars](https://img.shields.io/github/stars/worldbank/blackmarblepy)](https://github.com/worldbank/blackmarblepy)