`keybase pgp purge` asks the user to run an invalid command ("keybase decrypt <filename>") -- invalid because "keybase decrypt" expects input via STDIN

STEPS TO REPRODUCE:

1. Import a pgp private key into your keybase keychain.
2. Decide to purge that key, and run keybase pgp purge
   This gives the following output:

Exported PGP key files:
 1. /path/to/redacted/filename.saltpack

The PGP keys in the local Keybase keyring have been exported.
Please check that you have no problems decrypting them with

    keybase decrypt <filename>

and importing them into another keyring (like GPG).

Once you are confident that you have your keys in a safe place,
run this command with the -p flag:

    keybase pgp purge -p

to remove the keys from the local Keybase keyring.

3. Try to run the keybase decrypt command that you're instructed to run there, e.g. run this in your terminal:

keybase decrypt /path/to/redacted/filename.saltpack

ACTUAL RESULTS:
It doesn't work! It gives this error output:

Error parsing command line arguments: Command decrypt doesn't take any non-flag arguments

So, user stuck and is unable to purge their pgp key as they wanted to. User is sad and confused. :(

EXPECTED RESULTS:
Keybase should provide the user with a functional command to run, rather than a non-functional command. Either of these would work:

keybase decrypt < [filename]

...or:

cat [filename] | keybase decrypt

(Not sure whether <filename> with angle-brackets is the preferred placeholder here -- it's a bit confusing because < also happens to be "use-as-stdin" operator, which may actually need to be part of the 'Please run' command as noted above.)

VERSION INFO:
I have keybase version 1.0.18-20161202201411+495bb76 on 64-bit Ubuntu 16.04 (installed today, from the .deb linked from the keybase website)

Start by locating the user-facing message printed by keybase pgp purge, then verify the suggested command against keybase decrypt's stdin-only behavior. Done when purge prints a functional stdin-based command and the reproduction steps no longer produce the argument-parsing error.