Add cookbook recipe for removing a user from all sites in an org

Author: namespacebrian

docs/Cookbook.md

@@ -0,0 +1,15 @@
+# Cookbook
+
+Methods for common needs
+
+## Remove a user from all sites within an organization
+
+This can be accomplished with a shell one-liner:
+
+```bash
+for SITE in $(terminus org:site:list $ORG --format=string --field=name); do
+  terminus site:team:remove $SITE $EMAIL
+done
+```
+
+