title: add caption to flextable in docx
body: <p>How could one add a caption to a flextable rendered to docx? 
  EDIT: The aim is to produce a proper caption which can be referenced within the document to produce a list of tables and inline references.</p>
  
  <pre><code>iris.t &lt;-
    iris[1:5,] %&gt;%
    regulartable() %&gt;% 
    style(pr_c = officer::fp_cell(vertical.align = "bottom",
                                  border.bottom = officer::fp_border(width = 2)), part = "header") %&gt;% 
    rotate(j = names(iris)[-c(1:2)],
           rotation = "tbrl", part = "header", align = "bottom") %&gt;% 
    height(height = max(dim_pretty(., part = "header")$widths), part = "header") %&gt;% 
    width(width = dim_pretty(.,part = "body")$widths)
  
  iris.t 
  </code></pre>