:help nvim-tree-root-and-cwd

[alex-courtis]

tree.open, tree.toggle, tree.find_file and update focused file behaviour has many scattered options to control their behaviour.

Add a help section to outline all these options and API parameters and how they relate to each other.

Also cover actions.change_dir, sync_root_with_cwd, prefer_startup_root, respect_buf_cwd

See #2062 (comment)