Added a nice GitHub badge to show if the lab is being built correctly or not.

Author: dfreniche

README.md

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+[![.github/workflows/deploy.yml](https://github.com/mongodb-developer/aggregation-pipeline-lab/actions/workflows/deploy.yml/badge.svg?branch=main)](https://github.com/mongodb-developer/aggregation-pipeline-lab/actions/workflows/deploy.yml)
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+
 # Aggregation Pipeline Lab
 
 You can access the online version [here](https://mongodb-developer.github.io/aggregation-pipeline-lab/)