Add lang + ref tags to frontmatter

Those are fields used by the language switcher to correlate pages across
different languages, even if they have different names/paths/titles.
They are generated with the prepare_for_translation.py script.

external/os-guides/windows/windows-tools.md

@@ -1,4 +1,5 @@
 ---
+lang: en
 layout: doc
 redirect_from:
 - /doc/windows-tools/
@@ -12,5 +13,6 @@ redirect_from:
 - /doc/WindowsTools/
 - /wiki/WindowsTools/
 redirect_to: https://github.com/Qubes-Community/Contents/blob/master/docs/os/windows/windows-tools.md
+ref: 86
 title: Qubes Windows Tools
 ---

external/os-guides/windows/windows-vm.md

@@ -1,7 +1,9 @@
 ---
+lang: en
 layout: doc
 redirect_from:
 - /doc/windows-vm/
 redirect_to: https://github.com/Qubes-Community/Contents/blob/master/docs/os/windows/windows-vm.md
+ref: 85
 title: Installing a Windows VM
 ---