Add ChangeLog.

Add ChangeLog, which briefly summarizes releases.

Edit README and INSTALL.
diff --git a/jemalloc/README b/jemalloc/README
index 2ff36ef..4d7b552 100644
--- a/jemalloc/README
+++ b/jemalloc/README
@@ -1,9 +1,9 @@
 jemalloc is a general-purpose scalable concurrent malloc(3) implementation.
 This distribution is a stand-alone "portable" implementation that currently
-targets only Linux.  jemalloc is included as the default allocator in the
-FreeBSD and NetBSD operating systems, and it is used by the Mozilla Firefox web
-browser on Microsoft Windows-related platforms.  Depending on your needs, one
-of the other divergent versions may suit your needs better than this
+targets Linux and Apple OS X.  jemalloc is included as the default allocator in
+the FreeBSD and NetBSD operating systems, and it is used by the Mozilla Firefox
+web browser on Microsoft Windows-related platforms.  Depending on your needs,
+one of the other divergent versions may suit your needs better than this
 distribution.
 
 The COPYING file contains copyright and licensing information.
@@ -11,4 +11,6 @@
 The INSTALL file contains information on how to configure, build, and install
 jemalloc.
 
+The ChangeLog file contains a brief summary of changes for each release.
+
 URL: http://www.canonware.com/jemalloc/