title: Azure DevOps pipeline enter variable value from UI
body: <p>I want user to enter value of the variable before click on Run pipeline button</p>
  
  <p>I have empty variable in <code>pipeline.yml</code>:</p>
  
  <pre><code>- name: projectName
    value:
  </code></pre>
  
  <p>But UI doesn't show it:</p>
  
  <p><a href="https://i.stack.imgur.com/2Lou5.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/2Lou5.png" alt="enter image description here"></a></p>
  
  <p>How should I define var for user's input? </p>