Update user docs for pinentry vs clipboard

With #11239 (closed) solved, it is now possible to paste passwords into pinentry that were copied to the clipboard. This might be worth mentioning as an alternative to KeePassX + auto-type.

Related issues

Related to #11239 (closed)

Original created by @anonym on 11339 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information