* Add customizable list of command that triggers lazy loading

* Add $NVM_LAZY_CMD

* Add instruction to `NVM_LAZY_CMD` in README.md

It wasn’t clear where I should set the `NVM_AUTOLOAD` variable. The clue was to be found in [the docs for another plugin](https://github.com/ohmyzsh/ohmyzsh/tree/master/plugins/fzf). It seems setting values need to come before Oh My Zsh is sourced.

Updated read me to reflect this, and the fact that one of the settings mentioned is specific to nvm, not this plugin.

Closes #5782
Fixes #8959
Closes #8976

Co-authored-by: Marc Cornellà <marc.cornella@live.com>