content: improve wording for imports tab
content: improve wording for imports tab

The wording for the imports tab headers are imporved in this CL.

Change-Id: Id0815846ded65b049f3078921efaf4f83abbade5
Reviewed-on: https://team-review.git.corp.google.com/c/golang/discovery/+/532169
Reviewed-by: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite