add nvim-tree support, readme tuning

[emmanueltouzery]

the nvim-tree support seems to work. I didn't test it thoroughly yet, but it's looking good for now.

i also fixed the link to config.lua in the readme: that file doesn't exist anymore.

thanks for the plugin! i kept hoping i'd stop "holding it wrong", and kind of accepted now that this plugin will actually be helpful for me even in the long term :blush:

[stevearc]

Thanks for the PR!