Added slides link

Author: spalle1997

labs/lab_06.md

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 # Lab 6
 
-[Slides in PDF format](lab_06_slides.pdf)
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 You'll work in your [Project teams](../docs/project.md#teams).
 
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 ## Submit
 
 [Submit links to the pull request(s) via CourseWorks.](https://courseworks2.columbia.edu/courses/233896/assignments)
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+# [Slides](https://docs.google.com/presentation/d/1huYoR5yUwsrVkk2cWg-KHzn8Slygt2jv6ig2gdKekKE/edit?usp=sharing)