task qc readme: add develop branch instructions

Author: oliche

task_qc_viewer/README.md

@@ -17,6 +17,8 @@ Otherwise, activate the iblenv as described in the guide above.
 Go into the iblapps directory that you cloned:
 ```
 cd /home/olivier/Documents/PYTHON/iblapps/task_qc_viewer
+git checkout develop
+git pull
 ```
 Launch the Viewer by typing `ipython task_qc.py session_UUID` , example:
 ```