Update setup_your_environment.md (denoland#9876)

unlike other system config file, in windows `$profile` file is a 
common config file of powershell , just use `>` will override
the user config file , which is terrible. This change use append
instead of override which is more reasonable

docs/getting_started/setup_your_environment.md

@@ -69,7 +69,7 @@ command will be `antigen bundle deno` and so on.
 Example (Powershell):
 
 ```shell
-deno completions powershell > $profile
+deno completions powershell >> $profile
 .$profile
 ```