Update README.md

Author: nfahlgren

README.md

@@ -1,18 +1,15 @@
-# Thresholding (a.k.a. segmentation) Tutorials
+# Image Segmentation - Part 1: Thresholding
 
 [![test-pr](https://github.com/danforthcenter/plantcv-tutorial-threshold/actions/workflows/ci-tests.yml/badge.svg)](https://github.com/danforthcenter/plantcv-tutorial-threshold/actions/workflows/ci-tests.yml)
 
-Introduction to using thresholding tools with PlantCV.
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-
 [![Binder](https://mybinder.org/badge_logo.svg)](https://mybinder.org/v2/gh/danforthcenter/plantcv-tutorial-threshold/HEAD?labpath=index.ipynb)
 
+[![Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/danforthcenter/plantcv-tutorial-threshold/blob/main/index-colab.ipynb)
+
 [![Static Badge](https://img.shields.io/badge/Open%20in%20GitHub-black?logo=github)](https://github.com/danforthcenter/plantcv-tutorial-threshold)
 
 ## Tutorial tags/keywords
 
 thresholding, segmentation, masking
 
 ## Citations
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-