I believe normal String fields, like the Task description, is in plain text and will not read hyper links. If your requirements are flexible enough, you could possibly add a URL field. You could even change/add the description String field to an HTML and add a link tag.
In regards to the advanced script in the Workflow activity:
If URL: current.description = 'www.link.com'
If HTML: current.description = '<a href='link.com'>Click to move</a>'
