title: Button to add entry column to r shiny datatable
body: <p>I am looking to find a way to add a button to a datatable in r shiny that: 
  Adds an empty column to the data table each time it is clicked (and dataframe that made the table in the first place 
  Which the user can fill himself 
  With numeric or text values 
  And set their own column name to describe the type of entry values. </p>
  
  <p>To for instance add lab note records to instrument data that is already in the shiny app manually </p>
  
  <p>I am asking in case a more skilled person who has a better clue than me knows how to do this. 
  I have read a bunch of pages, but at best the example I found provides 1 fixed empty column with a fixed name</p>
  
  <blockquote>
    <p><a href="https://www.google.it/url?sa=t&amp;source=web&amp;rct=j&amp;url=https://stackoverflow.com/questions/33601291/make-a-column-in-a-basic-shiny-datatable-that-accepts-numeric-inputs&amp;ved=2ahUKEwibzejb5PbYAhVMCewKHdHBDogQjjgwA3oECBMQAQ&amp;usg=AOvVaw2L4AtNgRaGRmQXHR8AyyX0" rel="nofollow noreferrer">empty column</a></p>
  </blockquote>
  
  <p>A dummy table from the package : 
  library(DT)</p>
  
  <pre><code>ui &lt;- basicPage(
    h2("The mtcars data"),
    DT::dataTableOutput("mytable")
  )
  
  server &lt;- function(input, output) {
    output$mytable = DT::renderDataTable({
      mtcars
    })
  }
  
  shinyApp(ui, server)
  </code></pre>