Context menu will be no problem. I will also have it so that the commands will only be enabled if they can be used. So if you want to annotate a selection, you must have a selection for it to not be grayed out etc. All commands will still be available via the command palette as well. Maybe down the road I will consolidate them into a quick panel menu.
I will also add a little status message in the status bar letting you know you are in Annotation Mode.
I will try to get it into tonight. Documentation might happen later if I am lazy.