Add a members field to each file under _coops

I've populated the data, where available, from the field "Number of
current members The number of full members (owners) in the co-op." in
the wordpress admin.

_coops/dtc-innovation.md

@@ -1,6 +1,7 @@
 ---
 title: dtc innovation
 name: dtc innovation
+members: 3
 website: https://dtc-innovation.org/
 email: contact@dtc-innovation.org
 twitter: dtc-innovation