title: how to make group items in recyclerview using header
body: <p>I want to set group header in recyclerview,which means i have an api which contains json objects based on Lessons for example Lesson1 contains more than 3 items Lesson 2 contains 4 items.I already got response from api and displayed into recyclerview like this.</p>
  
  <pre><code>Lesson 1:
  Lesson 1:Random Numbers
  Lesson 1:Complex Numbers
  Lesson 1:Matrix
  </code></pre>
  
  <p>-</p>
  
  <pre><code>Lesson 2:
  Lesson 2:Algebra
  Lesson 2:Differentiation
  Lesson 2:Integration 
  </code></pre>
  
  <p>Like this i displayed into recyclerview .I want to group header display like</p>
  
  <pre><code>Lesson 1:
  Random Numbers
  Complex Numbers
  Matrix
  </code></pre>
  
  <p>-</p>
  
  <pre><code>Lesson 2:
  Algebra
  Differentiation
  Integration 
  </code></pre>
  
  <p>want to set header and group the items please help me frnds</p>