Add link to llvm git documentation, and recommend always building libcxx on OSX

[mclow.lists]

This looks fine to me. I think this should be committed.

[hintonda]

Thanks Marshall.

Btw, I don't have commit access, so if approved, could someone commit this for me?

www/get_started.html

 <p>Clang is released as part of regular LLVM releases. You can download the release versions from <a href="http://llvm.org/releases/">http://llvm.org/releases/</a>.</p>
 <p>Clang is also provided in all major BSD or GNU/Linux distributions as part of their respective packaging systems. From Xcode 4.2, Clang is the default compiler for Mac OS X.</p>
 
 <h2 id="build">Building Clang and Working with the Code</h2>
 
 <h3 id="buildNix">On Unix-like Systems</h3>
 
 <p>If you would like to check out and build Clang, the current procedure is as
-follows:</p>
+follows (instructions for using git can be found <a href="http://llvm.org/docs/GettingStarted.html#git-mirror">here</a>):</p>
 
 <ol>
   <li>Get the required tools.
   <ul>
     <li>See
       <a href="http://llvm.org/docs/GettingStarted.html#requirements">
       Getting Started with the LLVM System - Requirements</a>.</li>
     <li>Note also that Python is needed for running the test suite.
<ol>
   <li>Checkout Compiler-RT:
   <ul>
     <li><tt>cd llvm/projects</tt></li>
     <li><tt>svn co http://llvm.org/svn/llvm-project/compiler-rt/trunk
         compiler-rt</tt></li>
     <li><tt>cd ../..</tt></li>
   </ul>
   </li>
-  <li>Checkout libcxx: (only required to build and run Compiler-RT tests on OS X, optional otherwise)
+  <li>Checkout libcxx: (recommended for OS X, and required to build and run Compiler-RT tests on OS X, optional otherwise)
   <ul>
     <li><tt>cd llvm/projects</tt></li>
     <li><tt>svn co http://llvm.org/svn/llvm-project/libcxx/trunk
         libcxx</tt></li>
     <li><tt>cd ../..</tt></li>
   </ul>
   </li>
   <li>Build LLVM and Clang: