Add a label to Nativescript Marketplace for plugins/tools that aren't free

[razorsyntax]

Make sure to check the existing issues in this repository

Please, tell us what's the problem?

[ ] A typo
[ ] Wrong documentation
[ ] Improvement of existing article
[X ] Missing documentation
[ ] New article needed

Please, tell us more details

With many Nativescript Plugins being sold through 3rd-parties (like ProPlugins) we should ensure that the Nativescript Marketplace labels those plugins that are free and those that are not free.