Just to expand a bit, I realised that the explanation on the blogpage about the plugin, is subtly slightly better than the plugin page itself.
But the real standard for instructions for Tagger is this page: https://buildingonbubble.com/block/tagger-plugin-for-mentions-1515412723033x963917052088942600 which I see you wrote @NigelG, which is kinda ironic. 
Basically what you have written seems like good instructions with examples. Thanks! 