Move to incubating project (#1565)

We are in incubating stage now:
https://lists.cncf.io/g/cncf-toc/topic/result_coredns_moving_to/12935200?p=,,,20,0,0,0::recentpostdate%2Fsticky,,,20,2,0,12935200Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

README.md

@@ -11,7 +11,7 @@
 CoreDNS (written in Go) chains [plugins](https://coredns.io/plugins). Each plugin performs a DNS
 function.
 
-CoreDNS is a [Cloud Native Computing Foundation](https://cncf.io) inception level project.
+CoreDNS is a [Cloud Native Computing Foundation](https://cncf.io) incubating level project.
 
 CoreDNS is a fast and flexible DNS server. The keyword here is *flexible*: with CoreDNS you
 are able to do what you want with your DNS data by utilizing plugins. If some functionality is not