update chPick pres1

2019/2019-09-09_testCourseAdv/slides/chPickPresentation1.md

 ## Cherry Picking Workshop
 
-* In your branch, create a reference file
+* In your branch, create and commit a reference file
 ```bash
 $ echo "This is the start of a commit chain" > reference.txt
+$ git add reference.txt
+$ git commit origin myBranchName
 ```
 
 * Create and commit two files in the develop branch