WIP:  Content Experiments Documentation

See draft documentation at:  http://draft-nested-components.readthedocs.org/en/latest/organizing_course.html#nested-components
s/b "Enter a group configuration name," "Enter a name in the **Group Configuration Name** field," or "In the **Group Configuration Name** field, enter a name for your group configuration." (It's the same rule that applies in common nouns vs. titles: "Nagy is a professor at Harvard" vs. "Professor Nagy is at Harvard.")