Updated documentation contributed by Christopher Jefferson.

llvm-svn: 153955
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 6e3e78acbab6d53771667e75b12e0757a2b3d0c6
diff --git a/www/index.html b/www/index.html
index 9c0eee3..db10b92 100644
--- a/www/index.html
+++ b/www/index.html
@@ -146,7 +146,9 @@
   <p>
      On Mac OS 10.7 (Lion), the easiest way to get this library is to install
      Xcode 4.2 or later.  However if you want to install tip-of-trunk from here
-     (getting the bleeding edge), read on.
+     (getting the bleeding edge), read on.  However, be warned that Mac OS
+     10.7 will not boot without a valid copy of <code>libc++.1.dylib</code> in
+     <code>/usr/lib</code>.
   </p>
 
   <p>To build on Mac OS X 10.6 (Snow Leopard), you need a helper library and header