Document libFuzzer on Windows.

Summary:
Document that libFuzzer supports Windows, how to get it,
and its limitations.

Reviewers: kcc, morehouse, rnk, metzman

Reviewed By: kcc, rnk, metzman

Subscribers: hans, rnk

Differential Revision: https://reviews.llvm.org/D57597

llvm-svn: 353551
diff --git a/llvm/docs/LibFuzzer.rst b/llvm/docs/LibFuzzer.rst
index b322726..eb68f12 100644
--- a/llvm/docs/LibFuzzer.rst
+++ b/llvm/docs/LibFuzzer.rst
@@ -646,10 +646,20 @@
 using more external dependencies we will slow down the fuzzer while the main
 reason for it to exist is extreme speed.
 
-Q. What about Windows then? The fuzzer contains code that does not build on Windows.
+Q. Does libFuzzer Support Windows?
 ------------------------------------------------------------------------------------
 
-Volunteers are welcome.
+Yes, libFuzzer now supports Windows. Initial support was added in r341082.
+Any build of Clang 9 supports it. You can download a build of Clang for Windows
+that has libFuzzer from
+`LLVM Snapshot Builds <https://llvm.org/builds/>`_.
+
+Using libFuzzer on Windows without ASAN is unsupported. Building fuzzers with the
+`/MD` (dynamic runtime library) compile option is unsupported. Support for these
+may be added in the future. Linking fuzzers with the `/INCREMENTAL` link option
+(or the `/DEBUG` option which implies it) is also unsupported.
+
+Send any questions or comments to the mailing list: libfuzzer(#)googlegroups.com
 
 Q. When libFuzzer is not a good solution for a problem?
 ---------------------------------------------------------