Update README.md

README.md

@@ -3,7 +3,7 @@
 
 # imgproxy-rails
 
-TBD
+Integration of [imgproxy.rb](https://github.com/imgproxy/imgproxy.rb) with [ActiveStorage::Variant API](https://api.rubyonrails.org/v5.2.0/classes/ActiveStorage/Variant.html).
 
 ## Installation
 
@@ -19,9 +19,43 @@ gem "imgproxy-rails"
 - Ruby (MRI) >= 2.7.0
 - JRuby >= 9.2.9
 
+### Supported Rails versions
+- Rails >= 6.0.0
+
 ## Usage
 
-TBD
+Given the following configuration:
+
+```ruby
+# development.rb
+config.active_storage.resolve_model_to_route = :rails_storage_proxy
+
+# production.rb
+config.active_storage.resolve_model_to_route = :imgproxy_active_storage
+```
+The following HTML snippet will generate different URLs in dev and prod:
+
+```ruby
+# show.erb.html
+<%= image_tag Current.user.avatar.variant(resize: "100x100") %>
+```
+In dev, it will generate a URL like this:
+
+```html
+<img src="http://localhost:3000/rails/active_storage/blobs/proxy/eyJfcmFpbHMiOnsibWVzc2FnZSI6IkJBaHBBWHc9IiwiZXhwIjpudWxsLCJwdXIiOiJibG9iX2lkIn19--0c35e9a616c29da2dfa10a385bae7172526e7961/me.png">
+```
+In prod, it will generate a URL like this:
+
+```html
+<img src="https://imgproxy.example.com/8uVB2dYrZVOdG-1tekFjNJZ7s7VHDViXJbu9TcQavQ8/fn:me.png/aHR0cDovL2xvY2Fs/aG9zdDozMDAwL3Jh/aWxzL2FjdGl2ZV9z/dG9yYWdlL2Jsb2Jz/L3Byb3h5L2V5SmZj/bUZwYkhNaU9uc2li/V1Z6YzJGblpTSTZJ/a0pCYUhCQldIYzlJ/aXdpWlhod0lqcHVk/V3hzTENKd2RYSWlP/aUppYkc5aVgybGtJ/bjE5LS0wYzM1ZTlh/NjE2YzI5ZGEyZGZh/MTBhMzg1YmFlNzE3/MjUyNmU3OTYxL21l/LnBuZw">
+```
+
+You can also specify imgproxy-specific parameters in `imgproxy_options` attribute. Imgproxy-specific params will take precedence over ones from original API:
+
+```ruby
+# height=50 and width=50 will be applied
+Current.user.avatar.variant(resize: "100x100", imgproxy_options: { height: 50, width: 50 })
+```
 
 ## Contributing