Remove FAQ entries about the legacy license structure and add the most obvious FAQ entry for the new one.

[chandlerc]

Summary

Not sure what else we should be putting here, but I'm happy for anyone
to add questions they'd like answered here, and if I can, I'll add them
with an answer.

We could consider moving some of FAQ-like discussion from the developer
policy here or vice-versa if folks desire. Just let me know.

llvm/docs/FAQ.rst

 ================================
 Frequently Asked Questions (FAQ)
 ================================
 
 .. contents::
    :local:
 
 
 License
 =======
 
-Does the University of Illinois Open Source License really qualify as an "open source" license?
------------------------------------------------------------------------------------------------
-Yes, the license is `certified
-<http://www.opensource.org/licenses/UoI-NCSA.php>`_ by the Open Source
-Initiative (OSI).
+
+Why are there LLVM exceptions to the Apache 2.0 license?
+--------------------------------------------------------
+The LLVM exceptions address two potential issues users might have with using
+the Apache License 2.0. First, there are some concerns around combining code
+under Apache 2.0 with GPLv2 that the exceptions address. Second, the exceptions
+ensure LLVM-based runtime libraries don't impose Apache 2.0 notice requirements
+on software when you simply use LLVM as part of compiling that software. We
+designed this to be more flexible than usual because LLVM often shares code and
+technology between many different subsystems including runtime libraries and we
+don't want license terms to be a barrier to good engineering decisions around
+factoring out common logic.
 
 
 Can I modify LLVM source code and redistribute the modified source?
 -------------------------------------------------------------------
 Yes.  The modified source distribution must retain the copyright notice and
 follow the three bulleted conditions listed in the `LLVM license
 <http://llvm.org/svn/llvm-project/llvm/trunk/LICENSE.TXT>`_.