MAINTAINERS: add entries for some documentation scripts

There are some documentation scripts I wrote with doesn't
have any maintainer at maintainer's file.

Add them to the DOCUMENTATION entry, in order to have
Jon and linux-doc ML c/c on those patches, plus a new
entry to ensure that I'll be c/c when people send patches
to those.

Signed-off-by: Mauro Carvalho Chehab <[e-mail]>
Signed-off-by: Jonathan Corbet <[e-mail]>

MAINTAINERS

···
 L:	[e-mail]
 S:	Maintained
 F:	Documentation/
+F:	scripts/documentation-file-ref-check
 F:	scripts/kernel-doc
+F:	scripts/sphinx-pre-install
 X:	Documentation/ABI/
 X:	Documentation/firmware-guide/acpi/
 X:	Documentation/devicetree/
···
 L:	[e-mail]
 S:	Maintained
 F:	Documentation/translations/it_IT
+
+DOCUMENTATION SCRIPTS
+M:	Mauro Carvalho Chehab <[e-mail]>
+L:	[e-mail]
+S:	Maintained
+F:	scripts/documentation-file-ref-check
+F:	scripts/sphinx-pre-install
+F:	Documentation/sphinx/parse-headers.pl
 
 DONGWOON DW9714 LENS VOICE COIL DRIVER
 M:	Sakari Ailus <[e-mail]>