In the get started page, also explain how to start the testsuite

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@282402 91177308-0d34-0410-b5e6-96231b3b80d8

www/get_started.html

@@ -118,6 +118,11 @@ follows:</p>
     <li><tt>clang file.c -S -O3 -o -</tt> (output native machine code)</li>
   </ul>
   </li>
+  <li>Run the testsuite:
+  <ul>
+    <li><tt>make check-clang</tt></li>
+  </ul>
+  </li>
 </ol>
 
 <p>If you encounter problems while building Clang, make sure that your LLVM