Fix TTRSS recipe (#117)

manuscript/recipes/piwik.md

@@ -41,7 +41,7 @@ services:
     image: mysql
     volumes:
       - /var/data/piwik/mysql/runtime:/var/lib/mysql
-    env_file: /var/data/piwik/piwik.env
+    env_file: /var/data/config/piwik/piwik.env
     networks:
     - internal
   app:
@@ -90,4 +90,4 @@ networks:
 
 Launch the Piwik stack by running ```docker stack deploy piwik -c <path -to-docker-compose.yml>```
 
-Log into your new instance at https://**YOUR-FQDN**, and follow the wizard to complete the setup.
+Log into your new instance at https://**YOUR-FQDN**, and follow the wizard to complete the setup.