headers accept json code example

Example: accept header json

`Accept Header` can be used to ask the server to return
different type of response format 

For example :  

`/api/xname` endpoint , support both xml and json 
as response type so we can add accept header
`application/xml` to get xml result and `application/json` result. 

If server does not support such type ,
it will return `406 not acceptable` status code.