Trim down the XP notice and say more about what we support.

The big notice at the top of the release note is not interesting
 to most users now and apparently comes across poorly to some.

Better to provide more information about what we do support.

doc/release-notes.md

@@ -19,24 +19,16 @@ To receive security and update notifications, please subscribe to:
 Compatibility
 ==============
 
-Microsoft ended support for Windows XP on [April 8th, 2014](https://www.microsoft.com/en-us/WindowsForBusiness/end-of-xp-support),
+Bitcoin Core is extensively tested on multiple operating systems using
-an OS initially released in 2001. This means that not even critical security
+the Linux kernel, macOS 10.8+, and Windows Vista and later.
-updates will be released anymore. Without security updates, using a bitcoin
+
-wallet on a XP machine is irresponsible at least.
+Microsoft ended support for Windows XP on [April 8th, 2014](https://www.microsoft.com/en-us/WindowsForBusiness/end-of-xp-support).
-
+No attempt is made to prevent installing or running the software on Windows XP, you
-In addition to that, with 0.12.x there have been varied reports of Bitcoin Core
+can still do so at your own risk but be aware that there are known instabilities.
-randomly crashing on Windows XP. It is [not clear](https://github.com/bitcoin/bitcoin/issues/7681#issuecomment-217439891)
+Please do not report issues about Windows XP to the issue tracker.
-what the source of these crashes is, but it is likely that upstream
+
-libraries such as Qt are no longer being tested on XP.
+Bitcoin Core should also work on most other Unix-like systems but is not
-
+frequently tested on them.
-We do not have time nor resources to provide support for an OS that is
-end-of-life. From 0.13.0 on, Windows XP is no longer supported. Users are
-suggested to upgrade to a newer version of Windows, or install an alternative OS
-that is supported.
-
-No attempt is made to prevent installing or running the software on Windows XP,
-you can still do so at your own risk, but do not expect it to work: do not
-report issues about Windows XP to the issue tracker.
 
 Notable changes
 ===============