Add 1.6.0 release notes (#3044)

* Add 1.6.0 release notes

Preliminary notes for the 1.6.0 release
Signed-off-by: Miek Gieben <miek@miek.nl>

* Update notes/coredns-1.6.0.md
Co-Authored-By: Michael Grosser <development@stp-ip.net>

* Update notes/coredns-1.6.0.md
Co-Authored-By: Michael Grosser <development@stp-ip.net>

notes/coredns-1.6.0.md

++++
+title = "CoreDNS-1.6.0 Release"
+description = "CoreDNS-1.6.0 Release Notes."
+tags = ["Release", "1.6.0", "Notes"]
+release = "1.6.0"
+date = 2019-07-03T07:35:47+01:00
+author = "coredns"
++++
+
+The CoreDNS team has released
+[CoreDNS-1.6.0](https://github.com/coredns/coredns/releases/tag/v1.6.0).
+
+The `-cpu` flag is removed from this version.
+
+This release sports changes in the *file* plugin. A speed up in the *log* plugin and fixes in the
+*cache* plugin.
+
+Upcoming deprecation: the kubernetes *federation* plugin will be moved to
+github.com/coredns/federation. This is likely to happen in CoreDNS 1.7.0.
+
+# Plugins
+
+* The [*file*](/plugins/file) a lot of bug fixes and it loads lazily on start, i.e. if the zonefile
+  does not exist, it keeps trying with every reload period.
+* The [*cache*](/plugins/cache) fixes a race.
+* Multiple fixes in the [*route53*](/plugins/route53).
+* And the [*kubernetes*](/plugins/kubernetes) removes the `resyncperiod` option.
+
+## Brought to You By
+
+* Wonderful people
+
+## Noteworthy Changes
+
+plugin/file: Simplify locking (https://github.com/coredns/coredns/pull/3024)
+plugin/file: New zone should have zero records (https://github.com/coredns/coredns/pull/3025)
+plugin/file: Rename do to walk and cleanup and document (https://github.com/coredns/coredns/pull/2987)
+plugin/file: Fix setting ReloadInterval (https://github.com/coredns/coredns/pull/3017)
+plugin/file: Make non-existent file non-fatal (https://github.com/coredns/coredns/pull/2955)
+plugin/metrics: Fix response_rcode_count_total metric (https://github.com/coredns/coredns/pull/3029)
+pkg/cache: Fix race in Add() and Evict() (https://github.com/coredns/coredns/pull/3013)
+plugin/route53: Fix IAM credential file (https://github.com/coredns/coredns/pull/2983)
+plugin/route53: Fix multiple credentials in route53 (https://github.com/coredns/coredns/pull/2859)
+pkg/replacer: Evaluate format once and improve perf by ~3x (https://github.com/coredns/coredns/pull/3002)
+plugin/log: Fix log plugin benchmark and slightly improve performance (https://github.com/coredns/coredns/pull/3004)
+core: Scrub: TC bit is always set (https://github.com/coredns/coredns/pull/3001)
+plugin/rewrite: Fix domain length validation (https://github.com/coredns/coredns/pull/2995)
+plugin/kubernetes: Remove resyncperiod (https://github.com/coredns/coredns/pull/2923)