should use & to load completions for PowerShell (rust-lang#1978)

Author: hycinth22

Diff for: src/building/suggested.md

@@ -314,7 +314,7 @@ Zsh support will also be included once issues with [`clap_complete`](https://cra
 
 You can use `source ./src/etc/completions/x.py.<extension>`
 to load completions for your shell of choice,
-or `source .\src\etc\completions\x.py.ps1` for PowerShell.
+or `& .\src\etc\completions\x.py.ps1` for PowerShell.
 Adding this to your shell's startup script (e.g. `.bashrc`) will automatically load this completion.
 
 [`src/etc/rust_analyzer_settings.json`]: https://github.com/rust-lang/rust/blob/master/src/etc/rust_analyzer_settings.json