Initial set of release notes for 1.6.8 (#3728)

Signed-off-by: Miek Gieben <miek@miek.nl>

notes/coredns-1.6.8.md

++++
+title = "CoreDNS-1.6.8 Release"
+description = "CoreDNS-1.6.8 Release Notes."
+tags = ["Release", "1.6.8", "Notes"]
+release = "1.6.8"
+date = 2020-03-06T10:00:00+00:00
+author = "coredns"
++++
+
+The CoreDNS team has released
+[CoreDNS-1.6.8](https://github.com/coredns/coredns/releases/tag/v1.6.8).
+
+Again a small release with some nice improvements in the *forward* plugin, and overall polish.
+See "Noteworthy Changes" for more detail.
+
+Note that 1.7.0 will contain a bunch of backward incompatible changes: the *federation* plugin will
+be full removed and the metrics name will be changed to inline with the naming recommendation from
+the Prometheus project.
+
+## Brought to You By
+
+Andy Bursavich,
+Chris O'Haver,
+Christian Tryti,
+Kohei Yoshida,
+LongKB,
+Miek Gieben,
+Ricky S,
+Sylvain Rabot,
+Zou Nengren.
+
+## Noteworthy Changes
+
+* plugin/cache: explain drop metric (https://github.com/coredns/coredns/pull/3706)
+* plugin/forward: Add configuration flag to set if RecursionDesired should be set on health checks (https://github.com/coredns/coredns/pull/3679)
+* plugin/hosts: Modifies NODATA handling (https://github.com/coredns/coredns/pull/3536)
+* plugin/kubernetes: fix metadata (https://github.com/coredns/coredns/pull/3642)
+* plugin/kubernetes: Return all records with matching IP for reverse queries (https://github.com/coredns/coredns/pull/3687)
+* plugin/metrics: Add query type to latency as well (https://github.com/coredns/coredns/pull/3685)
+* plugin/pkg/up: Make default intervals shorter (https://github.com/coredns/coredns/pull/3651)
+* plugins/forward: Add max_concurrent option (https://github.com/coredns/coredns/pull/3640)
+* plugn/forward: Add exponential backoff to healthcheck (https://github.com/coredns/coredns/pull/3643)