docs: update autocompletion docs

docs/getting-started.md

@@ -70,7 +70,7 @@ or [running tasks](/tasks/)
 this step is not necessary. You can use it to make sure `mise` is correctly setup.
 :::
 
-Install `node` and set it as the global default:
+As an example, here is how you can install `node` and set it as the global default:
 
 ```sh
 mise use --global node@22

docs/installing-mise.md

@@ -344,7 +344,13 @@ mise completion bash > /etc/bash_completion.d/mise
 ```
 
 ```sh [zsh]
-# This requires zsh to be configured. If you e.g. use oh-my-zsh, it should work out of the box.
+# If you use oh-my-zsh, there is a `mise` plugin. Update your .zshrc file with:
+# plugins=(... mise)
+
+# Otherwise, look where zsh search for completions with 
+echo $fpath | tr ' ' '\n'
+
+# if you installed zsh with `apt-get` for example, this will work:
 mkdir -p /usr/local/share/zsh/site-functions
 mise completion zsh  > /usr/local/share/zsh/site-functions/_mise
 ```