Add note about CSP connect-src and webpack-dev-server

README.md

@@ -174,6 +174,12 @@ you can set the `host` when running `./bin/webpack-dev-server` binstub:
 WEBPACKER_DEV_SERVER_HOST=0.0.0.0 ./bin/webpack-dev-server
 ```
 
+**Note:** You need to allow webpack-dev-server host as allowed origin for `connect-src` if you are running your application in a restrict CSP environment like Rails 5.2+. This can be done in Rails 5.2+ for development environment in the CSP initializer `config/initializers/content_security_policy.rb` with a snippet like this:
+
+```ruby
+  p_connect_src :self, :https, 'http://localhost:3035', 'ws://localhost:3035' if Rails.env.development?
+```
+
 **Note:** Don't forget to prefix `ruby` when running these binstubs on windows
 
 ### webpack configuration