[readme] note zsh-nvm's AUTO_USE option

Author: gimbo

README.md

@@ -247,7 +247,7 @@ If you're running a system without prepackaged binary available, which means you
 
 Homebrew installation is not supported. If you have issues with homebrew-installed `nvm`, please `brew uninstall` it, and install it using the instructions below, before filing an issue.
 
-**Note:** If you're using `zsh` you can easily install `nvm` as a zsh plugin. Install [`zsh-nvm`](https://github.com/lukechilds/zsh-nvm) and run `nvm upgrade` to upgrade.
+**Note:** If you're using `zsh` you can easily install `nvm` as a zsh plugin. Install [`zsh-nvm`](https://github.com/lukechilds/zsh-nvm) and run `nvm upgrade` to upgrade ([you can set](https://github.com/lukechilds/zsh-nvm#auto-use) `NVM_AUTO_USE=true` to have it automatically detect and use `.nvmrc` files).
 
 **Note:** Git versions before v1.7 may face a problem of cloning `nvm` source from GitHub via https protocol, and there is also different behavior of git before v1.6, and git prior to [v1.17.10](https://github.com/git/git/commit/5a7d5b683f869d3e3884a89775241afa515da9e7) can not clone tags, so the minimum required git version is v1.7.10. If you are interested in the problem we mentioned here, please refer to GitHub's [HTTPS cloning errors](https://help.github.com/articles/https-cloning-errors/) article.