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.

introduction/code-of-conduct.md

@@ -1,6 +1,8 @@
 ---
+lang: en
 layout: default
 permalink: /code-of-conduct/
+ref: 118
 title: Code of Conduct
 ---
 

introduction/contributing.md

@@ -1,10 +1,12 @@
 ---
+lang: en
 layout: doc
 permalink: /doc/contributing/
 redirect_from:
 - /en/doc/contributing/
 - /doc/ContributingHowto/
 - /wiki/ContributingHowto/
+ref: 125
 title: Contributing to the Qubes OS Project
 ---
 

introduction/experts.md

@@ -1,5 +1,7 @@
 ---
+lang: en
 layout: experts
 permalink: /experts/
+ref: 119
 title: Experts
 ---

introduction/faq.md

@@ -1,4 +1,5 @@
 ---
+lang: en
 layout: sidebar
 permalink: /faq/
 redirect_from:
@@ -10,6 +11,7 @@ redirect_from:
 - /en/doc/devel-faq/
 - /doc/DevelFaq/
 - /wiki/DevelFaq/
+ref: 124
 title: Frequently Asked Questions
 ---
 

introduction/intro.html

@@ -1,4 +1,5 @@
 ---
+lang: en
 layout: default
 permalink: /intro/
 redirect_from:
@@ -7,6 +8,7 @@ redirect_from:
 - /tour/#what-is-qubes-os
 - /about/
 - /en/about/
+ref: 126
 title: Introduction
 ---
 

introduction/reporting-bugs.md

@@ -1,4 +1,5 @@
 ---
+lang: en
 layout: doc
 permalink: /doc/reporting-bugs/
 redirect_from:
@@ -10,6 +11,7 @@ redirect_from:
 - /bugs/
 - /bug-report/
 - /bug-reports/
+ref: 121
 title: Reporting bugs and other issues
 ---
 

introduction/screenshots.md

@@ -1,10 +1,12 @@
 ---
+lang: en
 layout: default
 permalink: /screenshots/
 redirect_from:
 - /media/
 - /doc/QubesScreenshots/
 - /wiki/QubesScreenshots/
+ref: 123
 title: Screenshots
 ---
 

introduction/statistics.md

@@ -1,8 +1,10 @@
 ---
+lang: en
 layout: default
 permalink: /statistics/
 redirect_from:
 - /counter/
+ref: 127
 title: Statistics
 ---
 

introduction/support.md

@@ -1,4 +1,5 @@
 ---
+lang: en
 layout: sidebar
 permalink: /support/
 redirect_from:
@@ -10,6 +11,7 @@ redirect_from:
 - /doc/qubes-lists/
 - /doc/QubesLists/
 - /wiki/QubesLists/
+ref: 122
 title: Help, Support, Mailing Lists, and Forum
 ---
 

introduction/video-tours.html

@@ -1,6 +1,8 @@
 ---
+lang: en
 layout: default
 permalink: /video-tours/
+ref: 226
 title: Video Tours of Qubes OS
 ---