doc: move extensions.worktreeConfig to the right place

All config extensions are described in technical/repository-version.txt.
I made a mistake of adding it in config.txt instead. This patch moves
it back to where it belongs.

Since repository-version.txt is not part of officially generated
documents (it's not even part of DOC_HTML target), it's only visible
to developers who read plain .txt files. Let's include it in
gitrepository-layout.5 for more visibility. Some minor asciidoc fixes
are required in repository-version.txt to make this happen.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Documentation/gitrepository-layout.txt b/Documentation/gitrepository-layout.txt
index d501af9..366dee2 100644
--- a/Documentation/gitrepository-layout.txt
+++ b/Documentation/gitrepository-layout.txt
@@ -290,6 +290,8 @@
 worktrees/<id>/config.worktree::
 	Working directory specific configuration file.
 
+include::technical/repository-version.txt[]
+
 SEE ALSO
 --------
 linkgit:git-init[1],