title: Add the index of list to bind_rows?
body: <p>I have this data:</p>
  
  <pre><code>dat=list(structure(list(Group.1 = structure(3:4, .Label = c("A","B", "C", "D", "E", "F"), class = "factor"), Pr1 = c(65, 75)), row.names = c(NA, -2L), class = "data.frame"),NULL, structure(list( Group.1 = structure(3:4, .Label = c("A","B", "C", "D", "E", "F"), class = "factor"), Pr1 = c(81,4)), row.names = c(NA,-2L), class = "data.frame"))
  </code></pre>
  
  <p>I want to use combine using   <code>bind_rows(dat)</code> but keeping the index number as a varaible
  Output Include <code>Type([[1]]  and [[3]])</code></p>
  
  <pre><code>  type   Group.1     Pr1
  1   1      C          65
  2   1      D         75
  3   3      C         81
  4   3      D          4
  </code></pre>