Usage: -F option desc. not entirely correct

[mykhal]

usign -F option claims that the related string/data is a fingerprint. But it's not entirely correct, it's not a hash but just random bytes (in signify it's now internally named keynum). See e.g.:

• main.c: generate()
• tedu: signify shortcomings

OpenWrt keys page uses term Key-ID.

usign usage should not say

print key fingerprint of public/secret key or signature

but rather e.g.

• print key "fingerprint" (ID) of public/secret key or signature

[mykhal]

now I've realized it's just a mirror here