Revert "README: warn on prefer-method: link TNS-23"

This reverts commit 57e5658c8d9154711979019d85b279ad5f6898c9.

This commit was a mistake: it included work-in-progess development
which was not ready for release. Only the README change should have
been included.
Reapply README change from 57e5658c, reverted in 27194f2e
Do not recreate fnil on every usage

Originally part of commit 57e5658c, reverted in 27194f2e