Add link to new howto on writing backends.

llvm-svn: 16204
diff --git a/llvm/docs/index.html b/llvm/docs/index.html
index c1fc973..8255644 100644
--- a/llvm/docs/index.html
+++ b/llvm/docs/index.html
@@ -131,6 +131,9 @@
 <li><a href="WritingAnLLVMPass.html">Writing an LLVM Pass</a> - Information
 on how to write LLVM transformations and analyses.</li>
 
+<li><a href="WritingAnLLVMBackend.html">Writing an LLVM Backend</a> - Information
+on how to write LLVM backends for machine targets.</li>
+
 <li><a href="CodeGenerator.html">The LLVM Target-Independent Code
 Generator</a> - The design and implementation of the LLVM code generator.
 Useful if you are working on retargetting LLVM to a new architecture, designing