Add documentation for changes to bulk import

[svelle]

More of a note to myself.

We need to add documentation for the changes introduced to the bulk import with this PR:
mattermost/mattermost#14034

Basically the post object now has a new attribute called props which can contain message attachments.

[justinegeffen]

Awesome, thanks @svelle! This is a very helpful change. :)

[justinegeffen]

Hi @svelle. Wanted to follow up and find out whether you've had a chance to update the docs for this? If not, let me know what the change is and I'll be happy to sort it out. :)

[svelle]

Hi @svelle. Wanted to follow up and find out whether you've had a chance to update the docs for this? If not, let me know what the change is and I'll be happy to sort it out. :)

Hey @justinegeffen ,
I'm out for the long weekend because of Easter holidays. I'll get on to it this week (ideally before the release of the new server version ;))

[justinegeffen]

Thanks @svelle! I've opened this PR in the meantime and will sync up with you when you're back. :)