Suggestion to improve README for zsh installation.

[leochoo]

Note: If you're using zsh you can easily install nvm as a zsh plugin. Install zsh-nvm and run nvm upgrade to upgrade.

The above line should be under Installation, not Important Notes.

Following the instruction, on Mac OSX, zsh is a default and hence I was able to install (or more like add) zsh by adding nvm to the ~/.zshrc file, instead of doing any curl or wget like this doc suggests.

It would be great if this can be fixed since zsh-nvm does not explain about nvm installed in zsh at all.

[ljharb]

@leochoo if you do not do the curl/wget like the doc suggests, then you are using an unsupported installation mechanism, and i won't be able to help you with any issues you encounter.

[RCMainak]

@leochoo Can you please help test PR #2511. It has the potentials to resolve this issue.