MAINTAINERS: Add entry for bcachefs

bcachefs is a new copy-on-write filesystem; add a MAINTAINERS entry for
it.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

MAINTAINERS

@@ -3464,6 +3464,13 @@ W:	http://bcache.evilpiepirate.org
 C:	irc://irc.oftc.net/bcache
 F:	drivers/md/bcache/
 
+BCACHEFS
+M:	Kent Overstreet <kent.overstreet@linux.dev>
+L:	linux-bcachefs@vger.kernel.org
+S:	Supported
+C:	irc://irc.oftc.net/bcache
+F:	fs/bcachefs/
+
 BDISP ST MEDIA DRIVER
 M:	Fabien Dessenne <fabien.dessenne@foss.st.com>
 L:	linux-media@vger.kernel.org