Documentation: Update path to sysrq.txt

Commit 9d85025b0418 ("docs-rst: create an user's manual book") moved the
sysrq.txt leaving old paths in the kernel docs.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/Documentation/s390/Debugging390.txt b/Documentation/s390/Debugging390.txt
index 3df8bab..5ae7f86 100644
--- a/Documentation/s390/Debugging390.txt
+++ b/Documentation/s390/Debugging390.txt
@@ -2116,7 +2116,7 @@
 This is particularly useful for syncing disks unmounting & rebooting
 if the machine gets partially hung.
 
-Read Documentation/sysrq.txt for more info
+Read Documentation/admin-guide/sysrq.rst for more info
 
 References:
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