Fix v0.5.2.rst whatsnew text

[cwhanse]

Restoring text that was deleted by mistake

pvlib python pull request guidelines

Thank you for your contribution to pvlib python!

You may submit a pull request with your code at any stage of completion, however, before the code can be merged the following items must be addressed:

• Closes fix whatsnew problems #454
• Fully tested. Added and/or modified tests to ensure correct behavior for all reasonable inputs. Tests must pass on the TravisCI and Appveyor testing services.
• Code quality and style is sufficient. Passes git diff upstream/master -u -- "*.py" | flake8 --diff and/or landscape.io linting service.
• New code is fully documented. Includes sphinx/numpydoc compliant docstrings and comments in the code where necessary.
• Updates entries to docs/sphinx/source/api.rst for API changes.
• Adds description and name entries in the appropriate docs/sphinx/source/whatsnew file for all changes.

Please don't hesitate to ask for help if you're unsure of how to accomplish any of the above. You may delete all of these instructions except for the list above.

Brief description of the problem and proposed solution (if not already fully described in the issue linked to above):

[wholmgren]

thanks @cwhanse