Make the constraints option available

for "GraphQL::Constraint::Directive::Constraintを毎回記述する必要があり少々冗長なため、より簡潔に記述できるAPIを検討中です。"

see https://zenn.dev/mh4gf/articles/graphql-ruby-constraint-directive#fn-cee9-1

README.md

@@ -54,6 +54,29 @@ type Mutation {
 }
 ```
 
+*tips:* You can use shorthand `constraints:` option if you let your argument class include `GraphQL::Constraint::Directive::ConstraintArgumentKeyword` helper.
+
+```ruby
+# optional
+# in your argument class
+require 'graphql/constraint/directive/constraint_argument_keyword'
+
+module Types
+  class BaseArgument < GraphQL::Schema::Argument
+    include GraphQL::Constraint::Directive::ConstraintArgumentKeyword
+  end
+end
+```
+
+```ruby
+# optional
+class CreateBook < BaseMutation
+  argument :title, String,
+           required: true,
+           # shorthand for `directives: { GraphQL::Constraint::Directive::Constraint =>...`
+           constraints: { min_length: 1, max_length: 200 }
+```
+
 ## API
 ### String
 #### minLength

lib/graphql/constraint/directive/constraint_argument_keyword.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+module GraphQL
+  module Constraint
+    module Directive
+      module ConstraintArgumentKeyword
+        def initialize(name, type, desc = nil, **kwargs)
+          if kwargs.key?(:constraints)
+            constraints = kwargs.delete(:constraints)
+            if constraints
+              directives = kwargs.delete(:directives) || {}
+              constraint_directive = GraphQL::Constraint::Directive::Constraint
+              directives[constraint_directive] = constraints
+              kwargs[:directives] = directives
+            end
+          end
+
+          super
+        end
+      end
+    end
+  end
+end