Document -UseX64MakeAppx workaround

Author: andyleejordan

helpers.build.psm1

@@ -1212,6 +1212,10 @@ function Update-PathEnvironment {
 function Find-MakeAppx {
     [CmdletBinding()]
     param(
+        # When packaging in OneBranch, the MSIX is created on an x64 image for
+        # the arm64 package, and our tooling expects to use the architecture
+        # passed, so we have to override it here. It may be possible to
+        # workaround this in another way, but deferring further investigation.
         [switch]$UseX64MakeAppx
     )