docs/Shell-Completion: update Zsh completions docs for Linux

docs/Shell-Completion.md

@@ -34,14 +34,14 @@ If you are using Homebrew's `bash` as your shell (i.e. `bash` >= v4) you should
 
 ## Configuring Completions in `zsh`
 
-To make Homebrew's completions available in `zsh`, the Homebrew-managed `zsh/site-functions` path needs to be inserted into `FPATH` before initialising `zsh`'s completion facility. This is done by `brew shellenv`, so if you followed the post-Homebrew installation steps and have `eval "$(brew shellenv)"` in your `~/.zprofile`, all you need is add the following to your `~/.zshrc` if it's not already there:
+To make Homebrew's completions available in `zsh`, the Homebrew-managed `zsh/site-functions` path needs to be inserted into `FPATH` before initialising `zsh`'s completion facility. This is done by `brew shellenv`, so if you followed the post-Homebrew installation steps, `eval "$(brew shellenv)"` should be in your `~/.zprofile` (on macOS) or `~/.zshrc` (on Linux). All you need is add the following to your `~/.zshrc` if it's not already there, and, if you're on Linux, make sure it's placed after `eval "$(brew shellenv)"`:
 
 ```sh
 autoload -Uz compinit
 compinit
 ```
 
-Note that if you are using Oh My Zsh, it will call `compinit` for you when you source `oh-my-zsh.sh`. In this case, you should be all set without any additional configuration.
+Note that if you are using Oh My Zsh, it will call `compinit` for you when you source `oh-my-zsh.sh`. In this case, make sure `eval "$(brew shellenv)"` is called before sourcing `oh-my-zsh.sh` if you're on Linux, and you should be all set without any additional configuration.
 
 You may also need to forcibly rebuild `zcompdump`: