docs: sphinixfy gcov.txt and move to dev-tools

No textual changes beyond formatting.

Cc: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/MAINTAINERS b/MAINTAINERS
index 1e5460c..bb53779 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -5118,7 +5118,7 @@
 M:	Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
 S:	Maintained
 F:	kernel/gcov/
-F:	Documentation/gcov.txt
+F:	Documentation/dev-tools/gcov.rst
 
 GDT SCSI DISK ARRAY CONTROLLER DRIVER
 M:	Achim Leubner <achim_leubner@adaptec.com>