Add Link in Quick Launch bar of a Sharepoint Site/Subsites.

Add-PSSnapin Microsoft.SharePoint.PowerShell 

$SPWeb = Get-SPWeb "http://server:port/Site"

$LinkURL = "http://google.com"

$QuickLaunch = $SPWeb.navigation.quicklaunch

$Node = New-Object Microsoft.SharePoint.Navigation.SPNavigationNode("Google", $LinkURL, $true)

$SPSubsiteWeb.Navigation.QuickLaunch.AddAsLast($Node)

$SPSubsiteWeb.update()