title: start rule: <select from navigator or grammar> in antlr plugin in IntelliJ
body: <p>I have created simple grammar file in IntelliJ but failing to see any effect of Antlr plugin. When I open file in ANTLR preview, it says </p>
  
  <pre><code>start rule: &lt;select from navigator or grammar&gt;
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/3vMgl.png" rel="noreferrer"><img src="https://i.stack.imgur.com/3vMgl.png" alt="enter image description here"></a></p>
  
  <p>What is start rule? How to select it from navigator? How to select it from grammar?</p>