Should I put reading group coordination / participation on CV? I am an active participant in an academic reading group. I am co-coordinator, meaning I help pick topics, schedule talks, coordinate food, update the website, send emails, etc. I've also presented a couple times when we can't get presenters at the last minute. I think a link on my website is fine, but does this activity warrant a place on an academic CV?

(EDIT: I'm a second-year PhD student if that matters.)
Absolutely yes. This is an important and cool activity. You can write something like:

2016-18 Coordinator of Journal Club at XXX research group, YYY Dep. - Task: pick topics, schedule talks, present papers, on a weekly basis. 10 participants.