Show notice about preferred support if `@supportURL` exists

* Use a "Well done" notice so we don't scare people off.
* Make this dismissable... some chatter on USO had ppl complaining about those not being dismissable

Applies to #239
Slight message change to cancel some possible confusion

Applies to #239
Merge pull request #247 from Martii/Issue-239supportURLnotice

Show notice about preferred support if `@supportURL` exists