Update README.md point button at notebook

README.md

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 When starting an image-based phenotyping project, it is important to consider the project's end goals. This is important because the purposes of the project will determine the camera type, imaging layout, and will help to guide downstream analysis. For example, if the goal of the project is to quantify leaf temperature, you may want to take images where ambient temperature and humidity are controlled. This tutorial will help to do an analysis of thermal images. 
 
-[![Binder](https://mybinder.org/badge_logo.svg)](https://mybinder.org/v2/gh/danforthcenter/plantcv-tutorial-thermal/HEAD)
+[![Binder](https://mybinder.org/badge_logo.svg)](https://mybinder.org/v2/gh/danforthcenter/plantcv-tutorial-thermal/HEAD?labpath=index.ipynb)
 
 ## Tutorial tags/keywords