doc: add supported platforms description

Closes: #983

README.md

@@ -224,18 +224,7 @@ Run:
 
 ## Supported Platforms
 
-Microsoft Windows operating systems since Windows XP SP2. It can be built
-with either Visual Studio or MinGW. Consider using
-[Visual Studio Express 2010][] or later if you do not have a full Visual
-Studio license.
-
-Linux using the GCC toolchain.
-
-OS X using the GCC or XCode toolchain.
-
-Solaris 121 and later using GCC toolchain.
-
-AIX 6 and later using GCC toolchain (see notes).
+Check the [SUPPORTED_PLATFORMS file](SUPPORTED_PLATFORMS.md).
 
 ### AIX Notes
 
@@ -254,7 +243,6 @@ See the [guidelines for contributing][].
 [node.js]: http://nodejs.org/
 [GYP]: http://code.google.com/p/gyp/
 [Python]: https://www.python.org/downloads/
-[Visual Studio Express 2010]: http://www.microsoft.com/visualstudio/eng/products/visual-studio-2010-express
 [guidelines for contributing]: https://github.com/libuv/libuv/blob/master/CONTRIBUTING.md
 [libuv_banner]: https://raw.githubusercontent.com/libuv/libuv/master/img/banner.png
 [x32]: https://en.wikipedia.org/wiki/X32_ABI

SUPPORTED_PLATFORMS.md

@@ -0,0 +1,31 @@
+# Supported platforms
+
+|  System | Support type | Supported versions | Notes |
+|---|---|---|---|
+| GNU/Linux | Tier 1 | Linux >= 2.6.18 with glibc >= 2.5 | |
+| macOS | Tier 1 | macOS >= 10.7 | |
+| Windows | Tier 1 | Windows >= XP SP1 | MSVC 2008 and later are supported |
+| FreeBSD | Tier 1 | >= 9 (see note) | |
+| AIX | Tier 2 | >= 6 | Maintainer: @iWuzHere |
+| zOS | Tier 2 | ??? | Maintainer: @jBarz |
+| Linux with musl | Tier 2 | musl >= 1.0 | |
+| SunOS | Tier 3 | Solaris 121 and later | |
+| MinGW | Tier 3 | MinGW 32 (from mingw.org) and MinGW-w64 | |
+| Other | Tier 3 | N/A | |
+
+#### Note on FreeBSD 9
+
+While FreeBSD is supported as Tier 1, FreeBSD 9 will get Tier 2 support until
+it reached EOL, in December 2016.
+
+## Support types
+
+* **Tier 1**: Officially supported and tested with CI. Any contributed patch
+  MUST NOT break such systems. These are supported by @libuv/collaborators.
+
+* **Tier 2**: Officially supported, but not necessarily tested with CI. These
+  systems are maintained to the best of @libuv/collaborators ability,
+  without being a top priority.
+
+* **Tier 3**: Community maintained. These systems may inadvertently break and the
+  community and interested parties are expected to help with the maintenance.