Clarify behavior of DuplicateProperty linter
Clarify behavior of DuplicateProperty linter

There was some confusion about how smart this linter was at detecting
intentional duplicate properties. Add documentation emphasizing that the
check is dumb.

Change-Id: Ib29e0b3ac379e9a9e54012abc6cc5df87b45df03
Reviewed-on: http://gerrit.causes.com/36947
Tested-by: jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@causes.com>
Reviewed-by: Shane da Silva <6f6e68d1df92f30cb4b3ce35260ddf94a402f33d@causes.com>

ingdir/scss-lint,gajus/scss-lint,leseulsteve/scss-lint,baileyparker/scss-lint,ivantsepp/scss-lint,teoljungberg/scss-lint,bkeepers/scss-lint,gatero/scss-lint,davecarter/scss-lint,cih/scss-lint,chatzipan/scss-lint,dwayhs/scss-lint,philipgiuliani/scss-lint,golmansax/scss-lint