ensure cmtkgui module is in path

* should fix #3
Merge branch 'master' of github.com:jefferis/fiji-cmtk-gui

# By jefferis
# Via jefferis
* 'master' of github.com:jefferis/fiji-cmtk-gui:
  Fix CMTK_Registration install location
  Add note to README about how to update
  Fix bug expanding CMTK installer