restconf www-data group membership clarification

apps/restconf/README.md

@@ -2,6 +2,11 @@
 
 ### Installation using Nginx
 
+Ensure www-data is member of the CLICON_SOCK_GROUP (default clicon). If not, add it:
+```
+  sudo usermod -a -G clicon www-data
+```
+
 Define nginx config file: /etc/nginx/sites-available/default
 ```
 server {