Include entityid_endpoint in the example SAML2 configurations

[melanger]

All Submissions:

• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
  Yes, although there is a related issue Allow definition of metadata URL for SAML plugins #280
• Have you added an explanation of what problem you are trying to solve with this PR?
  Unclear README.
• Have you added information on what your changes do and why you chose this as your solution?
• Have you written new tests for your changes?
  No tests needed.
• Does your submission pass tests?
• This project follows PEP8 style guide. Have you run your code against the 'flake8' linter?
  Not needed.

[c00kiemon5ter]

Thanks!