Tighten the language around "working tree" and "worktree" in the
docs.
* ds/worktree-docs:
worktree: use 'worktree' over 'working tree'
worktree: use 'worktree' over 'working tree'
worktree: use 'worktree' over 'working tree'
worktree: use 'worktree' over 'working tree'
worktree: use 'worktree' over 'working tree'
worktree: use 'worktree' over 'working tree'
worktree: use 'worktree' over 'working tree'
worktree: extract checkout_worktree()
worktree: extract copy_sparse_checkout()
worktree: extract copy_filtered_worktree_config()
worktree: combine two translatable messages