contrib: add words on adding new plugins (#3057)
contrib: add words on adding new plugins (#3057)

* contrib: add words on adding new plugins

New plugins are usually dropped in one giant ball of code, add some
words on how this can be approached and made to work faster.

(will at least give us something to point at)

Signed-off-by: Miek Gieben <00b357f94cf3a1145a32703fb42e2d80418ab806@miek.nl>

* Update CONTRIBUTING.md

Co-Authored-By: Michael Grosser <05134426bcd175050b08193c02f14ccdafcca088@stp-ip.net>

* Update CONTRIBUTING.md

Co-Authored-By: Michael Grosser <05134426bcd175050b08193c02f14ccdafcca088@stp-ip.net>

* Update CONTRIBUTING.md

Co-Authored-By: Michael Grosser <05134426bcd175050b08193c02f14ccdafcca088@stp-ip.net>

* Update CONTRIBUTING.md

* Update CONTRIBUTING.md

Co-Authored-By: Michael Grosser <05134426bcd175050b08193c02f14ccdafcca088@stp-ip.net>

yongtang/coredns,johnbelamaric/coredns,coredns/coredns,miekg/coredns,johnbelamaric/coredns,miekg/coredns,chrisohaver/coredns