Use BusyBox httpd Dockerfile; document registry-based Coolify deploy

Dockerfile

@@ -1,3 +1,6 @@
-FROM nginx:alpine
-COPY . /usr/share/nginx/html
+FROM alpine:latest
+RUN apk add --no-cache busybox-extras && mkdir -p /var/www
+COPY . /var/www/
+WORKDIR /var/www
 EXPOSE 80
+CMD ["busybox-extras", "httpd", "-f", "-p", "80", "-h", "/var/www"]