Improve "write the first review" text

Summary: The current text is ambiguous and un-exciting. This patches makes it clear and enticing! Who doesn't want to be the first to do something?

Test Plan: {F5709205}

Reviewers: #discover_software_store, apol

Reviewed By: #discover_software_store, apol

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D10476