docs: sphinxify kmemleak.txt and move it to dev-tools

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/MAINTAINERS b/MAINTAINERS
index 2ffd7ed..b235e0d 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -6812,7 +6812,7 @@
 KMEMLEAK
 M:	Catalin Marinas <catalin.marinas@arm.com>
 S:	Maintained
-F:	Documentation/kmemleak.txt
+F:	Documentation/dev-tools/kmemleak.rst
 F:	include/linux/kmemleak.h
 F:	mm/kmemleak.c
 F:	mm/kmemleak-test.c