Remove optional phrasing from README

When stating preferred practices, we should always state them in terms
of the default. Users can investigate if they want to configure the
lint check.

Change-Id: I42d77586608eb8bcbf9e665b51fa4d28167c9254
Reviewed-on: https://gerrit.causes.com/32824
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>