Add advise to allow trigger builds on tags when using branches:only: (#589)
Add advise to allow trigger builds on tags when using branches:only: (#589)

As commented in https://help.appveyor.com/discussions/problems/3483-github-tag-push-doesnt-trigger-build#comment_38384095
and recently tested in https://github.com/jneira/dhall-haskell/commit/f5d44d036b2d009beb2b0c0d6a4ef6a708f9d968
appveyor/website,appveyor/website,appveyor/website