openpgp: mention paper backups

howto/openpgp.md

@@ -1307,3 +1307,10 @@ or remember.
 
 I find that this is overkill: GnuPG keyring are encrypted with a
 passphrase, and that should be enough for most purposes.
+
+Another approach is to [backup your key on paper](https://ariis.it/static/articles/handwritten-pgp-key/page.html). Beware that this
+approach is time-consuming and exposes your private key to an attacker
+with physical access. The hand-written approach is also possibly
+questionable, as you basically need to learn typography for that
+purpose. The author, here, basically designs their own font,
+essentially.