Add rescue_from description in README

Darren · Darren · commit add998987bac · 2018-08-10T12:42:28.000+08:00
diff --git a/README.md b/README.md
@@ -2183,7 +2183,7 @@ You can also rescue all exceptions with a code block and handle the Rack respons
 ```ruby
 class Twitter::API < Grape::API
   rescue_from :all do |e|
-    Rack::Response.new([ e.message ], 500, { 'Content-type' => 'text/error' }).finish
+    Rack::Response.new([ e.message ], 500, { 'Content-type' => 'text/error' })
   end
 end
 ```
@@ -2254,7 +2254,16 @@ class Twitter::API < Grape::API
 end
 ```
 
-The `rescue_from` block must return a `Rack::Response` object, call `error!` or re-raise an exception.
+By default, object returned by `rescue_from` would be taken as response message. It is suggested to call `error!` in the last line of `rescue_from` block. But you could return `String`, `Hash`, `Array`, `Rack::Response` or even `nil` as well.
+
+```ruby
+rescue_from(:all) { error!('error') }
+rescue_from(:all) { 'error' }
+rescue_from(:all) { { message: 'error' } }
+rescue_from(:all) { [500, 'error', { 'Content-Type' => 'text/error' }] }
+rescue_from(:all) { Rack::Response.new('error', 500) }
+rescue_from(:all) { nil } # response default_message and default_status
+```
 
 The `with` keyword is available as `rescue_from` options, it can be passed method name or Proc object.
 
