Reword intro to linter section in README
Reword intro to linter section in README

Now that `scss-lint` is more customizable, the wording of this section
was misleadingly suggestive that `scss-lint` was still opinionated.

Change the wording to say that the defaults are opinionated.

Change-Id: I28ea02b17361f5fc7bb3375862fc7eb69bf565a3
Reviewed-on: https://gerrit.causes.com/33622
Tested-by: jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@causes.com>
Reviewed-by: Shane da Silva <6f6e68d1df92f30cb4b3ce35260ddf94a402f33d@causes.com>

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