So to complete @colin answer.
Here is a link of a blog post earlier this month: New Software Options for the Mark II - Mycroft
written by @gez-mycroft (edit correct gez).
How it should work is you say " Hey mycroft install count" and it will install the new skill.
You can see the list of skills in Mycroft Marketplace
I have tried this but mycroft does not seem to understand.
Also one thing I am curious is what the symbols on the skills mean. The Blue Mycroft symbol on the top left it seems to mean it is working on the system. But if it has a green tick next on the top right then the skill does not work. if it has no symbols it clearly does not work. For example I notice that the installer skill has a green tick, and it does not work.
But in contrast, I ask it to tell me a joke but it does not work. So not sure if it this is a rule or a bug.
I have marked this as a bug: Does not tell jokes