[Clang][Doc] Added an open project for improving command line docs

[xgupta]

Summary

There seems to be a lot of documentation is missing
for different command line flags uses.
This create confusion with same looking options, better to
document clearly their uses.

[aaron.ballman]

Thank you, this is a great suggestion! Just some minor wording changes, but otherwise LGTM.

clang/www/OpenProjects.html

40–44

[xgupta]

address comment

[xgupta]

In D149405#4305856, @aaron.ballman wrote:

Thank you, this is a great suggestion! Just some minor wording changes, but otherwise LGTM.

Thanks.

clang/www/OpenProjects.html

<ul>
   <li><a href="https://llvm.org/docs/TableGen/">table generating</a>
       documentation where possible, such as for implementation limits or other
       target-specific information,</li>
   <li>adding documentation for currently
      <a href="https://github.com/llvm/llvm-project/blob/main/clang/include/clang/Basic/AttrDocs.td">
      undocumented attributes</a>,</li>
   <li>documenting <a href="https://github.com/llvm/llvm-project/blob/main/clang/include/clang/Basic/DiagnosticDocs.td">
       diagnostic group flags</a> (adding code examples of what is diagnosed, or
       other relevant information), or</li>
+  <li>improve existing and add missing documentation for
+      <a href=" https://clang.llvm.org/docs/ClangCommandLineReference.html">
+      clang command line flags</a>, generated from <a href="https://github.com/llvm/llvm-project/blob/main/clang/include/clang/Driver/Options.td">
+      clang/Driver/Options.td</a>,</li>
   <li>help with completing other missing documentation.</li>
 </ul>
 These projects are independent of each other.</li>
 
 <li><b>Complete the investigation into Clang's C conformance</b>: Clang's
 <a href="c_status.html">C status page</a> contain a number of entries marked as
 <code>Unknown</code>. Completing the investigation involves adding
 <a href="https://github.com/llvm/llvm-project/tree/main/clang/test/C">test