MAINTAINERS: add mailing list for man-pages

Nowadays, man-pages has an associated mailing list. Mention that list
in MAINTAINERS.

Signed-off-by: Michael Kerrisk <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

MAINTAINERS

···
 P:	Michael Kerrisk
 M:	[e-mail]
 W:	http://www.kernel.org/doc/man-pages
+L:	[e-mail]
 S:	Supported
 
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