Add import statement to tutorial

[janerigby]

In this tutorial:
pysynphot/doc/source/tutorials.rst
it would be extremely helpful to new users to add the import statement:
import pysynphot as S

As a brand-new user, it took me 10 minutes of googling to figure out what "S" is. The tutorial should include all import statements that are necessary for the tutorial to worl.

[pllim]

Hi. Thank you for your interest in this package.

There are such instructions under the index.html page of http://pysynphot.readthedocs.io/en/latest/ (about half way down) and at the start of the tutorials page, it asks user to look at that part of index.html first. However, I agree that it is not the most straightforward solution.

Feel free to open a pull request to suggest where in tutorials.rst to insert the import statement in a way that is clear to you.