Add note to hacking.html that running the test harness directly from …

…the command-line requires making sure the relevant files are generated first. Patch by Matt Fowles, with some minor modifications.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@154795 91177308-0d34-0410-b5e6-96231b3b80d8

www/hacking.html

@@ -211,8 +211,16 @@ <h3 id="testingWindows">Testing using Visual Studio on Windows</h3>
   <h3 id="testingCommands">Testing on the Command Line</h3>
   <!--=====================================================================-->
 
-  <p>To run all the tests from the command line, execute a command like
-  the following:</p>
+  <p>If you want more control over how the tests are run, it may
+  be convenient to run the test harness on the command-line directly. Before
+  running tests from the command line, you will need to ensure that
+  <tt>lit.site.cfg</tt> files have been created for your build.  You can do
+  this by running the tests as described in the previous sections. Once the
+  tests have started running, you can stop them with control+C, as the
+  files are generated before running any tests.</p>
+
+  <p>Once that is done, to run all the tests from the command line,
+  execute a command like the following:</p>
 
   <pre>
   python (path to llvm)\llvm\utils\lit\lit.py -sv