Edit in JSFiddle

<!-- Логический -->
<p><a href="twitter-logo.png" download>Twitter Logo</a></p>

<!-- Со значением -->
<p><a href="twitter-logo.png" download="Logo">Twitter Logo</a></p>
body {
  color: #666;
  font: 14px/24px "HelveticaNeue-Light", "Helvetica Neue Light", "Helvetica Neue", Helvetica, Arial, "Lucida Grande", Sans-Serif;
}
p {
  margin: 0 0 24px 0;
}
p:last-of-type {
  margin: 0;
}