Add Xamarin.Forms UserProfile tutorial

Content

• https://github.com/rhedgpeth/UserProfileDemo 

Tasks

• Reference repository in publishing playbook https://docs.couchbase.com/tutorials/tutorial-template/sample.html#publish-your-tutorial
• Update the card on tutorial landing page
  • https://docs.couchbase.com/tutorials/tutorial-template/sample.html#add-a-tutorial-card
  • Existing card https://github.com/couchbase/tutorials/blame/master/modules/ROOT/pages/index.adoc#L60-L89

Published URLs

• https://docs.couchbase.com/tutorials/index.html
• https://docs.couchbase.com/userprofile-couchbase-mobile/standalone/userprofile/xamarin/userprofile_basic.html
• https://docs.couchbase.com/userprofile-couchbase-mobile/sync/userprofile/xamarin/userprofile_sync.html