Since we EOL'd Explorer there is no simple way to create document links in Alfresco. There is an open issue
AKU-162 to support link creation actions in the Aikau Document Library but this is blocked without a REST API to call.
To complete this issue we should just provide a REST API (not the UI, just the REST API) for creating document links and deleting all links to a document.
There have previously been partner extensions to provide this capability for earlier versions of Alfresco (see http://www.alfresco.com/partners/solutions/formtek-file-linking-extension), there is also a GitHub project that does this (https://github.com/skomarica/alfresco-share-create-link) and I believe that the RM module also uses this capability. So there should be plenty of samples to review.