Merge pull request #4284 from MarisaJL/patch-9

Adding link to cell cycle tutorial

topics/single-cell/tutorials/scrna-case_basic-pipeline/tutorial.md

@@ -559,6 +559,10 @@ Next up, we're going to scale our data so that all genes have the same variance
 
 {% icon congratulations %} Congratulations! You have processed your object!
 
+> <comment-title></comment-title>
+> At this point, we might want to remove or regress out the effects of unwanted variation on our data. A common example of this is the cell cycle, which can affect which genes are expressed and how much material is present in our cells. If you’re interested in learning how to do this, then you can move over to the [Removing the Effects of the Cell Cycle]({% link topics/single-cell/tutorials/scrna-case_cell-cycle/tutorial.md %}) tutorial now – then return here to complete your analysis. 
+{: .comment}
+
 # Preparing coordinates
 
 We still have too many dimensions. Transcript changes are not usually singular - which is to say, genes were in pathways and in groups. It would be easier to analyse our data if we could more easily group these changes.