[docs] Update HTML pages to refer to CSS in a way that works locally and with Sphinx.

llvm-svn: 155153
diff --git a/llvm/docs/HowToAddABuilder.html b/llvm/docs/HowToAddABuilder.html
index 0de2dac..985b30e 100644
--- a/llvm/docs/HowToAddABuilder.html
+++ b/llvm/docs/HowToAddABuilder.html
@@ -6,7 +6,7 @@
   <title>
     How To Add Your Build Configuration To LLVM Buildbot Infrastructure
   </title>
-  <link rel="stylesheet" href="llvm.css" type="text/css">
+  <link rel="stylesheet" href="_static/llvm.css" type="text/css">
 </head>
 <body>