Add info about SI not working on old versions of fish (#6364)

Removed the pwsh part as it's no longer true

docs/terminal/shell-integration.md

@@ -25,7 +25,7 @@ By default, the shell integration script should automatically activate on suppor
 
 This standard, easy way will not work for some advanced use cases like in sub-shells, through a regular `ssh` session (when not using the [Remote - SSH extension](/docs/remote/ssh.md)) or for some complex shell setups. The recommended way to enable shell integration for those is [manual installation](#manual-installation).
 
->**Note**: On Windows, you'll need PowerShell 7 (pwsh) for shell integration support. You can install via [https://aka.ms/PSWindows](https://aka.ms/PSWindows).
+>**Note**: Automatic injection may not work on old versions of the shell, for example older versions of fish do not support the `$XDG_DATA_DIRS` environment variable which is how injection works. You may still be able to manually install to get it working.
 
 ### Manual installation