Make sample config just have the HS config

The other options are things people usually won't need or want to
set, so just keep it to the basics.

 * Rename config sample to match element-web
 * Update / simplify build instructions
 * Rename nginx config file to differentiate it from EC config

Dockerfile

@@ -9,7 +9,7 @@ RUN scripts/dockerbuild.sh
 FROM nginxinc/nginx-unprivileged:alpine
 
 COPY --from=builder /src/dist /app
-COPY config/default.conf /etc/nginx/conf.d/
+COPY config/nginx.conf /etc/nginx/conf.d/
 
 USER root