title: Add descriptions / comments to graphql arguments?
body: <p>Is it possible to add a description or a comment to the arguments that are accepted in a query with graphql?</p>
  
  <p>I have a Query as follows:</p>
  
  <pre><code>    field :users, types[Types::UserType] do
    description 'List of Users. Date parameters accepted in yyyy/mm/dd format.'
  
    # Required for date range search, accepts string (yyyy/mm/dd)
    argument :from_date, types.String, default_value: nil
  </code></pre>
  
  <p>as you can see, currently I'm adding the description of the parameters to the description of the field.  In the graphiql schema where it describes the types I see:</p>
  
  <pre><code>users(from_date: Stringto_date: Stringemail: Stringname: Stringoffset: Intlimit: Int): [UserType]
  </code></pre>
  
  <p>when I click on the from_date it describes a string.  Is there anyway to have it describe the format of the string? eg. "A string in yyyy/mm/dd format."</p>
  
  <p>Thanks!</p>