Less confusing documentation for torpassword

Summary:
The current documentation leads the reader to think hash-password is an other option.
This change is less confusing and make it clear how to use this option.

Backport of Core PR14804
Depends on D8000

Test Plan: Proof-reading

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D8001