build: Make sure historical release notes end up in distributions

Adds the historical release notes to release tarballs and windows
installers.

Makefile.am

@@ -16,7 +16,7 @@ OSX_FANCY_PLIST=$(top_srcdir)/contrib/macdeploy/fancy.plist
 OSX_INSTALLER_ICONS=$(top_srcdir)/src/qt/res/icons/bitcoin.icns
 OSX_PLIST=$(top_srcdir)/share/qt/Info.plist #not installed
 
-DIST_DOCS = $(wildcard doc/*.md)
+DIST_DOCS = $(wildcard doc/*.md) $(wildcard doc/release-notes/*.md)
 
 WINDOWS_PACKAGING = $(top_srcdir)/share/pixmaps/bitcoin.ico \
   $(top_srcdir)/share/pixmaps/nsis-header.bmp \