Added a section on user permissions to enable kanban changes to documentation

[nathank (Nathan Kershaw)]

After running into problems with my users being unable to move topics between tag columns via the Kanban view, I’ve added this section to the documentation:

@Discourse

Empowering your users

As the mechanism for moving topics between kanban columns is by changing the tag, you have to ensure that your target users can actually do this. Options:

1. Ensure your target users are @staff, @trust_level_4, or category moderators
2. Alter the post edit time site settings (this allows users to be able to change the title / tags for their own topics for a much longer time)
3. Make all the topics wikis (they will need to edit the wiki to change the tag though, which isn’t great)

(couldn’t put it on the topic due to it being closed).