Add user mentions

[xdxd121xdxd]

so you can do @user in the comment or card description, task: it should probably send a notification maybe also add as a card member - not sure

[RARgames]

Thanks for the idea - it is already on our shortlist.
Right now, we have many internal feature requests and some requests from out GitHub community that are in progress.
I'll try to look at this in the meantime (cannot give any promises).

If anyone is willing to make a PR on this, I'll review it and add it sooner.