Update the template to wrap text at 79 columns

_check_lines_wrapping() invalidates lines longer than 79 columns (which
matches the default value of flake8 max-line-length). This change makes
the text wrap recommendation in template.rst consistent with that test.

Change-Id: I2d6489ae74e5d6259eca87a8e18a9b23f3f2f523
Merge "Update the template to wrap text at 79 columns"