Add OX documentation

[jubalh]

Translate/adapt https://mov.im/?blog/debxwoody%40movim.eu/profanity-und-openpgp-for-xmpp-ox-YRMREh and put it in the userguide like existing omemo/otr/openpgp documentation.

@kaffeekanne can you comment here then I can assign you to the issue (can't assign random people by github).

[kaffeekanne]

Permission granted.

[jubalh]

In the meantime @DebXWoody wrote: https://profanity-im.github.io/blog/post/openpgp-for-xmpp-ox/

[jubalh]

@kaffeekanne any progress?

[jubalh]

profanity-im/profanity@411887e adds a man page profanity-ox-setup.