title: how to add a day to date column?
body: <p>I wanna add a day to all cells of this dataframe:</p>
  <pre><code>value       B   N   S      date   
  date                    
  2020-12-31  1   11  0   2020-12-31  
  2021-01-01  3   80  0   2021-01-01  
  2021-01-02  4   99  0   2021-01-02  
  2021-01-03  3   78  0   2021-01-03  
  2021-01-04  0   50  0   2021-01-04
  </code></pre>
  <p>to make it like this:</p>
  <pre><code>value       B   N   S      date   
  date                    
  2020-12-31  1   11  0   2021-01-01  
  2021-01-01  3   80  0   2021-01-02  
  2021-01-02  4   99  0   2021-01-03  
  2021-01-03  3   78  0   2021-01-04  
  2021-01-04  0   50  0   2021-01-05
  </code></pre>
  <p>how can I do this?</p>