added deadlettersinkuri set rules as must to brokers and channels spec (#86)
added deadlettersinkuri set rules as must to brokers and channels spec (#86)

* added deadlettersinkuri set rules as must to brokers and channels spec

* Update specs/eventing/control-plane.md

Co-authored-by: Evan Anderson <117bc6d2b27bb69c2d939d4326f66adf27abab12@gmail.com>

* fixed typos and grammar mistakes

Co-authored-by: Evan Anderson <117bc6d2b27bb69c2d939d4326f66adf27abab12@gmail.com>
knative/specs