Added cheatsheet to the schedule

schedule/workshop_schedule.md

@@ -35,6 +35,7 @@
 
 
 ## Post-class resources
+* [O2 Cheatsheet](../O2_cheatsheet.pdf)
 * [Practice exercises for using R on O2](../lessons/R_on_O2_class_exercises.md)
 
 *These materials have been developed by members of the teaching team at the [Harvard Chan Bioinformatics Core (HBC)](http://bioinformatics.sph.harvard.edu/). These are open access materials distributed under the terms of the [Creative Commons Attribution license](https://creativecommons.org/licenses/by/4.0/) (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.*