more examples

[gravesti]

Fixes #617

Submission Checklist

• Run unit tests
• Declare copyright holder and agree to license (see below)

Summary

Add examples for summary function.

Copyright and Licensing

Please list the copyright holder for the work you are submitting
(this will be you or your assignee, such as a university or company):
F. Hoffman-La Roche

By submitting this pull request, the copyright holder is agreeing to
license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
• Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

[rok-cesnovar]

Thank you @gravesti and apologies that this fell through the cracks and no one responded in a month.