Fix clang Visual Studio build instructions

[Loghorn]

Summary

Change cd ..\.. to cd llvm-project (the former is probably a leftover of the old svn instructions)

[rnk]

lgtm

[Loghorn]

Is there a chance this will ever be merged?

[amccarth]

I'll merge it for you.

Reviewers generally assume you have commit access and will submit it yourself unless tell them otherwise.

clang/www/get_started.html

<ol>
   </ul>
   <p><em>Note</em>: Some Clang tests are sensitive to the line endings.  Ensure
      that checking out the files does not convert LF line endings to CR+LF.  If
      you're using git on Windows, make sure your <tt>core.autocrlf</tt> setting
      is false.</p>
   </li>
   <li>Run CMake to generate the Visual Studio solution and project files:
   <ul>
-    <li><tt>cd ..\..</tt>  (back to where you started)</li>
+    <li><tt>cd llvm-project</tt></li>
     <li><tt>mkdir build</tt> (for building without polluting the source dir)</li>
     <li><tt>cd build</tt></li>
     <li>
       If you are using Visual Studio 2017:
       <tt>cmake -DLLVM_ENABLE_PROJECTS=clang -G "Visual Studio 15 2017" -A x64 -Thost=x64 ..\llvm</tt><br/>
       <tt>-Thost=x64</tt> is required, since the 32-bit linker will run out of memory.
     </li>
     <li>To generate x86 binaries instead of x64, pass <tt>-A Win32</tt>.</li>