Add deployment instructions for Brotli support

Author: clupprich

docs/deployment.md

@@ -44,6 +44,8 @@ Webpacker doesn't serve anything in production. You’re expected to configure y
 
 Some servers support sending precompressed versions of files with the `.gz` extension when they're available. For example, nginx offers a `gzip_static` directive.
 
+Some servers support sending precompressed versions of files when they're available. For example, nginx offers a `gzip_static` directive that serves files with the `.gz` extension to supported clients. With an optional module, nginx can also serve Brotli compressed files with the `.br` extension (see below for installation and configuration instructions).
+
 Here's a sample nginx site config for a Rails app using Webpacker:
 
 ```nginx
@@ -71,11 +73,24 @@ server {
 
   location ^~ /packs/ {
     gzip_static on;
+    brotli_static on; # Optional, see below
     expires max;
   }
 }
 ```
 
+### Installing the ngx_brotli module
+
+If you wanna serve Brotli compressed files with nginx, you need to install the `nginx_brotli` module. Installation instructions from source can be found in the official [google/ngx_brotli](https://github.com/google/ngx_brotli) repository. Alternatively, depending on your platform, the module might be available via a pre-compiled package.
+
+Once installed, you need to load the module. As we wanna serve pre-compressed files, we only need the static module. Add the following line to your `nginx.conf` file and reload nginx:
+
+```
+load_module modules/ngx_http_brotli_static_module.so;
+```
+
+Now you can set `brotli_static on;` in your nginx site config, per the config in the last section above.
+
 ## CDN
 
 Webpacker out-of-the-box provides CDN support using your Rails app `config.action_controller.asset_host` setting. If you already have [CDN](http://guides.rubyonrails.org/asset_pipeline.html#cdns) added in your Rails app
@@ -106,4 +121,3 @@ namespace :deploy do
   end
 end
 ```
-