feat(pyenv): silence bad config warning with `ZSH_PYENV_QUIET=true`

plugins/pyenv/README.md

-# pyenv 
+# pyenv
 
 This plugin looks for [pyenv](https://github.com/pyenv/pyenv), a Simple Python version
 management system, and loads it if it's found. It also loads pyenv-virtualenv, a pyenv
@@ -10,6 +10,11 @@ To use it, add `pyenv` to the plugins array in your zshrc file:
 plugins=(... pyenv)
 ```
 
+## Settings
+
+- `ZSH_PYENV_QUIET`: if set to `true`, the plugin will not print any messages if it
+  finds that `pyenv` is not properly configured.
+
 ## Functions
 
 - `pyenv_prompt_info`: displays the Python version in use by pyenv; or the global Python

plugins/pyenv/pyenv.plugin.zsh

 pyenv_config_warning() {
+  [[ "$ZSH_PYENV_QUIET" != true ]] || return 0
+
   local reason="$1"
   local pyenv_root="${PYENV_ROOT/#$HOME/\$HOME}"
   cat >&2 <<EOF