Add sdkman for installation on download page.

Author: marc0der

_layouts/downloadpage.html

@@ -83,6 +83,7 @@ <h2>Other ways to install Scala</h2>
                   <a id="download-binaries">Download the Scala binaries for <span id="users-os"></span></a>
                   <br/><span class="install"><a href="{{ site.baseurl }}/download/install.html">Need help running the binaries?</a></span>
                 </li>
+                <li>Use <a href="https://sdkman.io">SDKMAN!</a> for a convenient single-command CLI installation.</li>
                 <li>Use <a href="https://scastie.scala-lang.org">Scastie</a> to run single-file Scala programs in your browser using multple Scala compilers; the production Scala 2.x compilers, Scala.js, Dotty, and Typelevel Scala. Save and share executable Scala code snippets.</li>
                 <li>Try Scala in the browser via <a href="https://scalafiddle.io/">ScalaFiddle</a>. This lets you run single-file Scala programs in your browser using Scala.js, including graphical/interactive examples such as <a href="https://scalafiddle.io/sf/KOsXSKv/0">Oscilloscope</a> or <a href="https://scalafiddle.io/sf/4beVrVc/1">Ray Tracer</a></li>
                 <li><a href="http://ammonite.io/">Get Ammonite</a>, a popular Scala REPL</li>