.gitignore: Ignore release artifacts.

Not ignoring these in the tree leads to the next generated version (.version)
being suffixed with '-dirty', which confuses things.

* .gitignore [/guix-*]: New pattern.
[/doc/stamp-[0-9]]: Adjust to ...
[/doc/stamp-*]: ... this.
[/release-*]: New pattern.

.gitignore

@@ -75,7 +75,7 @@
 /etc/guix-publish.service
 /etc/init.d/guix-daemon
 /etc/openrc/guix-daemon
-/guix-daemon
+/guix-*
 /guix/config.scm
 /libformat.a
 /libstore.a
@@ -129,6 +129,7 @@
 /po/packages/remove-potcdate.sin
 /po/packages/stamp-po
 /pre-inst-env
+/release-*
 /scripts/guix
 /test-env
 /test-tmp
@@ -147,7 +148,7 @@ tmp
 /doc/os-config-lightweight-desktop.texi
 /nix/scripts/download
 /.version
-/doc/stamp-[0-9]
+/doc/stamp-*
 /gnu/packages/bootstrap
 /gnu/packages/aux-files/guile-guile-launcher.o
 /guile