* bootstrap: Substitute ‘guix-cookbook’ for copy/pasted ‘guix-manual’.

Reported-by: jetomit on #guix

* .gitignore: Update ignore list.
* Makefile.am (assert-no-store-file-names): Exclude the cookbook.
* bootstrap: Generate po files for cookbook translations.
* doc/guix-cookbook.texi: New file.
* doc/local.mk (info_TEXINFOS): Add it; add a rule to build cookbook
translations.
* po/doc/local.mk (DOC_COOKBOOK_PO_FILES): New variable.
(EXTRA_DIST): Add cookbook pot file and po files.
(doc-po-update-cookbook-%): New target.
(doc-pot-update): Also update cookbook pot file.
(doc-po-update): Also update cookbook po files.

* bootstrap: Generate stub files for the manual translations whose
generated files are not included in the VCS.
* doc/contributing.de.texi: Remove file.
* doc/contributing.es.texi: Remove file.
* doc/contributing.fr.texi: Remove file.
* doc/contributing.zh_CN.texi: Remove file.
* doc/guix.de.texi: Remove file.
* doc/guix.es.texi: Remove file.
* doc/guix.fr.texi: Remove file.
* doc/guix.zh_CN.texi: Remove file.
* .gitignore: Add them.

Signed-off-by: Julien Lepiller <julien@lepiller.eu>

* nix/sync-with-upstream: Remove.
* bootstrap: Remove uses of 'git submodule' and 'sync-with-usptream'.
* .gitmodules: Remove.

* bootstrap: Always run "git submodule init".  Run
  `nix/sync-with-upstream'.
  Reported by Nikita Karetnikov and Andreas Enge.

* bootstrap, nix/sync-with-upstream: New files.
* Makefile.am (EXTRA_DIST): Add `bootstrap'.
* daemon.am (EXTRA_DIST): Add `nix/sync-with-upstream'.