www documentation for using Polly with dragonegg.

Added a file that explains how to load Polly in dragonegg.
Also fixed a typo in the document for clang.

Committed with a typo fix and a change to make this website available from
the documentation section.

Contributed by: Sameer Sahasrabuddhe  <Sameer.Sahasrabuddhe@amd.com>

llvm-svn: 161928