Added volume declaration

Dockerfile

@@ -1,4 +1,5 @@
 FROM nginx:stable-alpine
+LABEL maintainer="William Miceli <git@williammiceli.me>"
 USER root
 
 ARG GRAV_VERSION
@@ -46,6 +47,8 @@ RUN sed -i 's/root \/home\/USER\/www\/html/root \/var\/www/g' /etc/nginx/conf.d/
     && sed -i '49clisten.mode = 0660' /etc/php7/php-fpm.d/www.conf \
     && sed -i 's/listen = 127.0.0.1:9000/listen = \/var\/run\/php-fpm.sock/g' /etc/php7/php-fpm.d/www.conf
 
+VOLUME /var/www/
+
 COPY /entrypoint.sh /
 
 EXPOSE 80