[luciexe/exe] Add some more useful package docs.
[luciexe/exe] Add some more useful package docs.

R=tandrii@chromium.org

Bug: 939368
Change-Id: I677853da5476593e4facd4e8eaac3d9059d28180
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/1817974
Commit-Queue: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Commit-Queue: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@google.com>
Auto-Submit: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Reviewed-by: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@google.com>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go