Add 1.6.4 release notes (#3315)

Automatically submitted.

notes/coredns-1.6.4.md

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+title = "CoreDNS-1.6.4 Release"
+description = "CoreDNS-1.6.4 Release Notes."
+tags = ["Release", "1.6.4", "Notes"]
+release = "1.6.4"
+date = 2019-09-27T10:00:00+00:00
+author = "coredns"
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+
+The CoreDNS team has released
+[CoreDNS-1.6.4](https://github.com/coredns/coredns/releases/tag/v1.6.4).
+
+Various code cleanups and documentation improvements. We've added one new plugin: *acl*, that allows
+blocking requests.
+
+# Plugins
+
+* [*acl*](/plugins/acl) block request from IPs or IP ranges.
+* [*kubernetes*](/plugins/kubernetes) received some bug fixes, see below for specific PRs.
+* [*hosts*](/plugins/hosts) exports metrics on the number of entries and last reload time.
+
+## Brought to You By
+
+An Xiao,
+Chris O'Haver,
+Cricket Liu,
+Guangming Wang,
+Kasisnu,
+li mengyang,
+Miek Gieben,
+orangelynx,
+xieyanker,
+yeya24,
+Yong Tang.
+
+## Noteworthy Changes
+
+* plugin/hosts: add host metrics (https://github.com/coredns/coredns/pull/3277)
+* plugin/kubernetes: Don't duplicate service record for every port (https://github.com/coredns/coredns/pull/3240)
+* plugin/kubernetes: Handle multiple local IPs and bind (https://github.com/coredns/coredns/pull/3208)
+* Add plugin ACL for source IP filtering (https://github.com/coredns/coredns/pull/3103)