feat: bash and (fi)zsh completion along with docs

autocomplete/powershell_autocomplete.ps1

@@ -0,0 +1,9 @@
+$fn = $($MyInvocation.MyCommand.Name)
+$name = $fn -replace "(.*)\.ps1$", '$1'
+Register-ArgumentCompleter -Native -CommandName $name -ScriptBlock {
+     param($commandName, $wordToComplete, $cursorPosition)
+     $other = "$wordToComplete --generate-bash-completion"
+         Invoke-Expression $other | ForEach-Object {
+            [System.Management.Automation.CompletionResult]::new($_, $_, 'ParameterValue', $_)
+         }
+ }