Enabling linkattrs explicitly on doc pages having external links

Asciidoc may fail to render link attributes for external links
supposed to open in a new window correctly. This change adds
:linkattrs: to the beginning of such files to force parsing link
attributes correctly.

Bug: Issue 12068
Change-Id: If18be60de646ff78f672239dd4fa435fd4fd92ab

Documentation/dev-community.txt

diff --git a/Documentation/dev-community.txt b/Documentation/dev-community.txt
index ed9eead..5892253 100644
--- a/Documentation/dev-community.txt
+++ b/Documentation/dev-community.txt
@@ -1,3 +1,4 @@
+:linkattrs:
 = Gerrit Community
 
 Gerrit is developed as a