title: Should use "sp" instead of "dp" for text sizes
body: <p>When I use</p>
  
  <pre><code>android:textSizes="20dp" 
  </code></pre>
  
  <p>in my XML for a <code>textView</code>, I got a warning "Should use <code>"sp"</code> instead of <code>"dp"</code> for text sizes." </p>
  
  <p>Why should "dp" not be used? What is the correct approach? How can I achieve same textsizes on different displays?</p>