Add deployment note in README

It's recommended to use `yarn install --frozen-lockfile` in a deployment
context prior to compiling assets for production. This practice may help
offset potential concerns with the removal of the yarn integrity check,
at least in production environemnts.

README.md

@@ -604,6 +604,7 @@ Webpacker::Compiler.watched_paths << 'bower_components'
 
 Webpacker hooks up a new `webpacker:compile` task to `assets:precompile`, which gets run whenever you run `assets:precompile`. If you are not using Sprockets, `webpacker:compile` is automatically aliased to `assets:precompile`. Similar to sprockets both rake tasks will compile packs in production mode but will use `RAILS_ENV` to load configuration from `config/webpacker.yml` (if available).
 
+When compiling assets for production on a remote server, such as a continuous integration environment, it's recommended to use `yarn install --frozen-lockfile` to install NPM packages on the remost host to ensure that the installed packages match the `yarn.lock` file.
 
 ## Docs