docs: update release doc with more merge details
docs: update release doc with more merge details

Added some additional details for how the caretaker should merge PRs, including a GitHub search which lists all pending PRs.

clydin/angular-cli,angular/angular-cli,catull/angular-cli,angular/angular-cli,ocombe/angular-cli,Brocco/angular-cli,beeman/angular-cli,filipesilva/angular-cli,DevIntent/angular-cli,filipesilva/angular-cli,hansl/angular-cli,geofffilippi/angular-cli,geofffilippi/angular-cli,Brocco/angular-cli,ocombe/angular-cli,ocombe/angular-cli,hansl/angular-cli,angular/angular-cli,DevIntent/angular-cli,filipesilva/angular-cli,beeman/angular-cli,angular/angular-cli,geofffilippi/angular-cli,hansl/angular-cli,manekinekko/angular-cli,catull/angular-cli,clydin/angular-cli,manekinekko/angular-cli,beeman/angular-cli,hansl/angular-cli,clydin/angular-cli,clydin/angular-cli,Brocco/angular-cli,DevIntent/angular-cli,catull/angular-cli,catull/angular-cli,manekinekko/angular-cli,DevIntent/angular-cli,filipesilva/angular-cli,Brocco/angular-cli,ocombe/angular-cli,beeman/angular-cli,Brocco/angular-cli,ocombe/angular-cli,DevIntent/angular-cli,geofffilippi/angular-cli