title: git: update the 2 branch after a merge
body: <p>This is a newbie question. I have 2 branches, <strong>branch_A</strong> and <strong>branch_B</strong>. I am in branch A and do a merge with this command:</p>
  
  <pre><code>git checkout branch_A
  git merge --commit -m "my commit" branch_B
  </code></pre>
  
  <p>If there is no conflict, it automatically does the merge and updates the branch_A to new commit. But branch_B is still in same place.</p>
  
  <p>How can I update the branch_B to point in same place than branch_A?</p>