Issue title: how can i  add last updated time of refresh in pullRefreshLayout just below the circle animatio ? 
 Issue body: @baoyongzhang  @edwardaa 

how can i  add last updated time of refresh in pullRefreshLayout just below the circle animatio ? 

 Comments: 
 Comment 0: download source code，add this function by youself.

{'source': 'GithubIssues', 'repo_name_with_owner': 'baoyongzhang/android-PullRefreshLayout', 'issue_id': 103654159, 'repo_stars': 2052.0}