Add helper message for tests (#648)

The way the tests work, it requires removing and re-adding the label. I
have seen a few trainees confused about this. This adds a little note
about it at the end.

---------

Co-authored-by: l <l>

Author: LonMcGregor

test-sdc.sh

@@ -180,3 +180,5 @@ elif [[ "$1" == "implement-cowsay" ]]; then
 else
 	echo "Please run this with a valid test directory name as argument"
 fi
+
+echo "If you want to re-run the automated tests after changing some code, remove the 'Needs Review' label, wait a little, and then re-add the 'Needs Review' label on your PR." >> testoutput.txt