Add service account to local group during installation

Membership in the group "Performance Monitor Users" is required for the
CPU load monitoring to work, so add the service account to this group.

Refers to #40

Scripts/Install-Service.ps1

@@ -64,6 +64,24 @@ function Install-Service {
 }
 
 
+function Add-PerfMonGroupMember {
+    $GroupName = "Performance Monitor Users"
+    try {
+        Add-LocalGroupMember -Group $GroupName -Member $ServiceUser
+        Write-Host $("Successfully added user [$($ServiceUser)] to the local"
+                     "group [$($GroupName)].")
+    }
+    catch [Microsoft.PowerShell.Commands.MemberExistsException] {
+        Write-Host $("User [$($ServiceUser)] is already a member of the local"
+                     "group [$($GroupName)], no action required.")
+    }
+    catch {
+        Write-Host $("Adding user [$($ServiceUser)] to the local group"
+                     "[$($GroupName)] failed: $($_.Exception.Message)")
+    }
+}
+
+
 $ErrorActionPreference = "Stop"
 
 
@@ -87,6 +105,7 @@ if ($Service) {
 
 Copy-ServiceFiles
 Install-Service
+Add-PerfMonGroupMember
 
 Write-Host "`nWatching the service log file can be done like this:`n" `
     "`n> Get-Content -Wait -Tail 50 $($ServiceLog)`n"