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.

developer/system/architecture.md

@@ -1,4 +1,5 @@
 ---
+lang: en
 layout: doc
 permalink: /doc/architecture/
 redirect_from:
@@ -6,6 +7,7 @@ redirect_from:
 - /en/doc/qubes-architecture/
 - /doc/QubesArchitecture/
 - /wiki/QubesArchitecture/
+ref: 56
 title: Architecture
 ---
 

developer/system/audio.md

@@ -1,6 +1,8 @@
 ---
+lang: en
 layout: doc
 permalink: /doc/audio-virtualization/
+ref: 60
 title: Audio Virtualization
 ---
 

developer/system/gui.md

@@ -1,4 +1,5 @@
 ---
+lang: en
 layout: doc
 permalink: /doc/gui/
 redirect_from:
@@ -6,6 +7,7 @@ redirect_from:
 - /en/doc/gui-docs/
 - /doc/GUIdocs/
 - /wiki/GUIdocs/
+ref: 61
 title: GUI
 ---
 

developer/system/networking.md

@@ -1,4 +1,5 @@
 ---
+lang: en
 layout: doc
 permalink: /doc/networking/
 redirect_from:
@@ -6,6 +7,7 @@ redirect_from:
 - /en/doc/qubes-net/
 - /doc/QubesNet/
 - /wiki/QubesNet/
+ref: 59
 title: Networking
 ---
 

developer/system/security-critical-code.md

@@ -1,4 +1,5 @@
 ---
+lang: en
 layout: doc
 permalink: /doc/security-critical-code/
 redirect_from:
@@ -6,6 +7,7 @@ redirect_from:
 - /doc/SecurityCriticalCode/
 - /wiki/SecurityCriticalCode/
 - /trac/wiki/SecurityCriticalCode/
+ref: 55
 title: Security-critical Code
 ---
 

developer/system/storage-pools.md

@@ -1,6 +1,8 @@
 ---
+lang: en
 layout: doc
 permalink: /doc/storage-pools/
+ref: 57
 title: Storage Pools
 ---
 

developer/system/system-doc.md

@@ -1,4 +1,5 @@
 ---
+lang: en
 layout: doc
 permalink: /doc/system-doc/
 redirect_from:
@@ -7,5 +8,6 @@ redirect_from:
 - /wiki/SystemDoc/
 redirect_to:
 - /doc/#developer-documentation
+ref: 62
 title: System Documentation
 ---

developer/system/template-implementation.md

@@ -1,10 +1,12 @@
 ---
+lang: en
 layout: doc
 permalink: /doc/template-implementation/
 redirect_from:
 - /en/doc/template-implementation/
 - /doc/TemplateImplementation/
 - /wiki/TemplateImplementation/
+ref: 58
 title: Template Implementation
 ---