Document Windows caveats (#1577)

CONTRIBUTING.md

@@ -74,3 +74,10 @@ provide as much information as possible that helps us reproduce the problem.
 Please be advised that metadata updates are prioritized over code changes,
 except for bug fixes. In addition, we work with a limited number of build
 systems and may not be able to support every setup.
+
+In particular, we don't actively maintain windows builds but would be able to
+accept a PR provided someone else in the open-source community could test it out
+and would be able to help with the review. One way to look for such
+collaborators would be to email the [discussion
+group](https://groups.google.com/group/libphonenumber-discuss). Also see the
+[known Windows issues](FAQ.md#what-about-windows).

FAQ.md

@@ -205,3 +205,22 @@ There is no RFC indicating where the data comes from, or what format they're in.
 We'd love to consume machine-readable numbering plan data (assigned ranges,
 carrier & geo mappings). If you can connect us with partners in the industry
 to achieve this, please do so. Thanks!
+
+## Builds
+
+### What about Windows?
+
+Unfortunately the libphonenumber team does not have the resources or expertise
+to maintain Windows-specific functionality of the C++ library. We list here some
+known issues that would benefit from open-source collaboration. If you can
+contribute a PR and/or review and test out someone else's PR, please chime in on
+these links, or email the [discussion
+group](https://groups.google.com/group/libphonenumber-discuss):
+
+*   PR [#1090](https://github.com/googlei18n/libphonenumber/pull/1090) /
+    [#824](https://github.com/googlei18n/libphonenumber/issues/824) to "Replace
+    POSIX directory operations by Boost Filesystem"
+*   [#1307](https://github.com/googlei18n/libphonenumber/issues/1307) to use
+    readdir instead of readdir_r
+*   [#1555](https://github.com/googlei18n/libphonenumber/issues/1555) to allow
+    Windows to build cpp library with pthreads for multi-threading