MAINTAINERS: Add maintainer entry for zstd

Adds a maintainer entry for zstd listing myself as the maintainer for
all zstd code, pointing to the upstream issues tracker for bugs, and
listing my linux repo as the tree.

Signed-off-by: Nick Terrell <terrelln@fb.com>

MAINTAINERS

@@ -20582,6 +20582,18 @@ F:	Documentation/vm/zsmalloc.rst
 F:	include/linux/zsmalloc.h
 F:	mm/zsmalloc.c
 
+ZSTD
+M:	Nick Terrell <terrelln@fb.com>
+S:	Maintained
+B:	https://github.com/facebook/zstd/issues
+T:	git git://github.com/terrelln/linux.git
+F:	include/linux/zstd*
+F:	lib/zstd/
+F:	lib/decompress_unzstd.c
+F:	crypto/zstd.c
+N:	zstd
+K:	zstd
+
 ZSWAP COMPRESSED SWAP CACHING
 M:	Seth Jennings <sjenning@redhat.com>
 M:	Dan Streetman <ddstreet@ieee.org>