MAINTAINERS: add Documentation/dev-tools/ to workflows@

The goal of the workflows@ mailing list was to make it easier for
maintainers who don't use lore+lei to subscribe to topics related
to process changes. In other words it should cover changes to Documentation
files which most maintainers should know about. Recent changes from Kees [1]
to provide guidelines on naming KUnit files did not fall under workflows@
since Documentation/dev-tools/ isn't covered. The patch volume for
dev-tools isn't huge and most of the changes are interesting. Add it.

Link: https://lore.kernel.org/[e-mail]/ # [1]
Signed-off-by: Jakub Kicinski <[e-mail]>
Reviewed-by: Kees Cook <[e-mail]>
Signed-off-by: Jonathan Corbet <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

MAINTAINERS

···
 M:	Jonathan Corbet <[e-mail]>
 L:	[e-mail]
 S:	Maintained
+F:	Documentation/dev-tools/
 F:	Documentation/maintainer/
 F:	Documentation/process/