notmuch: changed nomaintainer to rseichter

Added myself as the designated maintainer for Notmuch. Please see
#3971 (comment)
for reference.

Signed-off-by: Ralph Seichter <github@seichter.de>

mail/notmuch/Portfile

@@ -8,7 +8,7 @@ version             0.28.3
 categories          mail
 platforms           darwin
 license             GPL-3+
-maintainers         nomaintainer
+maintainers         {seichter.de:macports @rseichter} openmaintainer
 description         The mail indexer
 long_description    \"Not much mail\" is what Notmuch thinks about your email \
                     collection, even if you receive 12000 messages per month or have on the \