remove autocomplete command (#782)

Add a note in readme about adding shell completions

Closes: https://gitea.com/gitea/tea/issues/781
Co-authored-by: techknowlogick <techknowlogick@noreply.gitea.com>
Reviewed-on: https://gitea.com/gitea/tea/pulls/782
Reviewed-by: techknowlogick <techknowlogick@noreply.gitea.com>
Co-authored-by: TheFox0x7 <thefox0x7@gmail.com>
Co-committed-by: TheFox0x7 <thefox0x7@gmail.com>

contrib/autocomplete.ps1

@@ -1,9 +0,0 @@
-$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', $_)
-         }
- }