Add basic documentation to docker installation + initialize empty folders for themes and content

Dockerfile

@@ -10,19 +10,30 @@ RUN a2enmod rewrite \
 # Install PHP ext-gd
 RUN docker-php-ext-install gd
 
+# Copy app content
+# Use the .dockerignore file to control what ends up inside the image!
 WORKDIR /var/www/html
 COPY . .
 
+# Install server dependencies
 RUN chmod +x /var/www/html/docker-utils/install-composer && \
     /var/www/html/docker-utils/install-composer && \
     ./composer.phar update && \
     chmod +x /var/www/html/docker-utils/init-server
 
+# Expose useful volumes (see documentation)
 VOLUME /var/www/html/settings
-VOLUME /var/www/html/content
 VOLUME /var/www/html/media
-VOLUME /var/www/html/themes
 VOLUME /var/www/html/cache
 
-# Run the server
+# Create a default copy of content and theme in case of empty directories binding
+RUN mkdir -p /var/www/html/content.default/ && \
+    cp -R /var/www/html/content/* /var/www/html/content.default/ && \
+    mkdir -p /var/www/html/themes.default/ && \
+    cp -R /var/www/html/themes/* /var/www/html/themes.default/
+
+VOLUME /var/www/html/content
+VOLUME /var/www/html/themes
+
+# Inject default values if content and themes are mounted with empty directories, adjust rights and start the server
 CMD ["/var/www/html/docker-utils/init-server"]