Just checked with our moderation team. This would count as an invitation to send donations to the author, and is against our publishing policies. So it is not allowed. Thanks so much for checking with us first! We appreciate your diligence.
What is the purpose of the link? If it's to generate bitcoin payments for yourself then my guess would be no. However, I'm unsure if the help pages specifically addresses bitcoins but it would be worth checking out. As Lobobrandon says, it's a relatively new concept.