Added CDN-JS support

[smitpatelx]

Hey I submited this repo to wellknown cdn provider and now its time to add to getting started page:

https://cdnjs.com/libraries/vue-tour

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue-tour/1.6.0/vue-tour.umd.min.js" integrity="sha512-uAuPH2bRtMDXOaZVCyeaiD+nYrwR8yFQWk9Qu3KiMU1nVjSdQkkw60gIfoYHqtQa1/pnTWLy+Vo1lhV4jQU74w==" crossorigin="anonymous"></script>

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue-tour/1.6.0/vue-tour.common.js" integrity="sha512-0PsIi6EuMH2mfjNO++HJK6PQpkn6He2vwGbvlVItpOkf6Ea9Qo/A0n+ViWb+TP1cE+VkAStzl9tQQn6Y4Kf0MA==" crossorigin="anonymous"></script>

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue-tour/1.6.0/vue-tour.common.min.js" integrity="sha512-d/xxiS42v3gsXoZ2tnLfWP0twUp1/bfYNDFACPLSBrgZE2Na2D/GlaEP6zo79EpTsRPgyUdjYntj+7WOMR1C4A==" crossorigin="anonymous"></script>

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue-tour/1.6.0/vue-tour.umd.js" integrity="sha512-zogBmAi1pPOXELv8RKwHtrOXIb1qLhSgoPFlAbTg/gCG2v91bGrzHEK1+4vsEoMOHYiDdgRE8vbj58aR88RJFA==" crossorigin="anonymous"></script>

Also keep in mind, cdnjs team will be changing github repo to add this official repo (instead of mine). But that's not a problem, because cdn js is pulling data from npm. https://github.com/cdnjs/packages/pull/672

[HZooly]

Thanks for submission. Is it possible to include CSS file? We need CSS styles if we want Vue Tour to be smooth running.