Clarify wrangling demo instructions

Add clarification that trainee needs to be connected to the AWS instance before entering the shell commands (ie the shell commands are executed on the AWS instance, not locally).

_extras/teaching_demos.md

@@ -24,7 +24,7 @@ tar -xzf shell_data.tar.gz
 
 Use [these instructions](https://datacarpentry.org/genomics-workshop/AMI-setup/index.html) to launch and connect to your own instance of the Data Carpentry Genomics AMI. This instance should cost you approximately US $1.20 per day. (This cost estimate is provided without any guarantee of accuracy and Data Carpentry assumes no liability for costs associated with your AMI instance(s).)
 
-Follow the shell commands below to ensure that the data directory is created,
+Once you have connected to your AWS instance, use the shell commands below to ensure that the data directory is created,
 that the data is placed into the data directory, and that you are in the data directory before
 starting to operate on the data.