ghcd must include branch name to support worktrees

[indexzero]

Current

ghcd $ORG/$REPO # --> [[clone, cd], cd] $GITROOT/org/repo

Future

ghcd $ORG/$REPO         # --> [[clone, cd], cd] $GITROOT/org/repo/$DEFAULT_BRANCH
ghcd $ORG/$REPO/$BRANCH # --> [[clone, cd], cd] $GITROOT/org/repo/$DEFAULT_BRANCH \
                        #                         && git worktree $GITROOT/org/repo/$DEFAULT_BRANCH

Still some semantics to work through with the git worktree / $BRANCH support but fundamentally just using the branch name by default will make the repo & all worktrees have a common ancestor in the file system which has a number of benefits for configuring tooling.