title: how to add key variables to `dplyr::group_map()`?
body: <p>I have the following, but want to add the <code>group_by()</code> key <code>Species</code> to the resulting tibble:</p>
  <h3>MWE</h3>
  <pre><code>iris %&gt;% 
    group_by(Species) %&gt;% 
    group_map(~ broom::tidy(lm(Sepal.Length ~ Sepal.Width, data = .x))) %&gt;% 
    bind_rows()
  </code></pre>
  <h3>Output</h3>
  <pre><code># How do I add the grouping key `Species` to this?
  
    term        estimate std.error statistic  p.value
    &lt;chr&gt;          &lt;dbl&gt;     &lt;dbl&gt;     &lt;dbl&gt;    &lt;dbl&gt;
  1 (Intercept)    2.64     0.310       8.51 3.74e-11
  2 Sepal.Width    0.690    0.0899      7.68 6.71e-10
  3 (Intercept)    3.54     0.563       6.29 9.07e- 8
  4 Sepal.Width    0.865    0.202       4.28 8.77e- 5
  5 (Intercept)    3.91     0.757       5.16 4.66e- 6
  6 Sepal.Width    0.902    0.253       3.56 8.43e- 4
  </code></pre>