title: How to add percentage to "unknown" in gtsummary
body: <p>I have a continuous variable with a significant proportion of unknowns. My advisor is asking me to put the percentage next to it in the column. This reprex mimics  what I am trying to do.</p>
  <pre><code>library(tidyverse)
  library(gtsummary)
  
    trial %&gt;%       # included with gtsummary package
    select(trt, age, grade) %&gt;%
    tbl_summary()
  </code></pre>
  <p>I am trying to have the percentage of unknowns listed next to unknown, ideally in parentheses. It would look like 11 (5.5%).</p>
  <p>Some have replied with a request for how the missing data appears in my dataset, here is a reprex of that</p>
  <pre><code>library(gtsummary)
  library(tidyverse)
  #&gt; Warning: package 'tibble' was built under R version 4.0.3
  #&gt; Warning: package 'readr' was built under R version 4.0.3
  library(gtsummary)
  
  df&lt;-
    tibble::tribble(
                 ~age,       ~sex,  ~race,          ~weight,
    70, &quot;male&quot;,  &quot;white&quot;,       50,
    57, &quot;female&quot;, &quot;african-american&quot;,   87,
    64,  &quot;male&quot;,  &quot;white&quot;,              NA,
    46,  &quot;male&quot;,  &quot;white&quot;, 49,
    87,  &quot;male&quot;,  &quot;hispanic&quot;, 51
    )
  
  df %&gt;%
    select(age,sex,race,weight) %&gt;%
    tbl_summary(type = list(age ~ &quot;continuous&quot;, weight ~ &quot;continuous&quot;), missing=&quot;ifany&quot;)
  </code></pre>