docs: sphinxify kasan.txt and move to dev-tools

No textual changes beyond formatting.

Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Acked-by: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/MAINTAINERS b/MAINTAINERS
index bb53779..2ffd7ed 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -6587,7 +6587,7 @@
 S:	Maintained
 F:	arch/*/include/asm/kasan.h
 F:	arch/*/mm/kasan_init*
-F:	Documentation/kasan.txt
+F:	Documentation/dev-tools/kasan.rst
 F:	include/linux/kasan*.h
 F:	lib/test_kasan.c
 F:	mm/kasan/