Tips on Mayavi2 import errors are outdated

```
Traceback (most recent call last):
File "/Users/penny/anaconda/envs/mayavi2/bin/mayavi2", line 6, in
sys.exit(main())
File "/Users/penny/anaconda/envs/mayavi2/lib/python2.7/site-packages/mayavi/scripts/mayavi2.py", line 646, in main
'''
ImportError: Could not import backend for traits
Make sure that you have either the TraitsBackendWx or the TraitsBackendQt
projects installed. If you installed Mayavi with easy_install, try easy_install
. easy_install Mayavi[app] will also work.
```

However `TraitsBackendWx` and/or `TraitsBackendQt` are superseded by `traitsui` + `pyface` + one of wxpython/pyqt4/pyside

Please see original message in #460