Update README.s390

The link to the "z/Architecture Principles of Operation" document is out
of date.  Update it.

diff --git a/README.s390 b/README.s390
index 86f867188a7e996800a4196077818d55fcfd2694..528eafc5ccd345759953d6825924856a2607382a 100644 (file)
--- a/README.s390
+++ b/README.s390
@@ -42,6 +42,6 @@ Reading Material
 (1) ELF ABI s390x Supplement
     https://github.com/IBM/s390x-abi/releases
 (2) z/Architecture Principles of Operation
-    https://www.ibm.com/support/pages/zarchitecture-principles-operation
-(3) z/Architecture Reference Summary
-    https://www.ibm.com/support/pages/zarchitecture-reference-summary
+    https://publibfp.dhe.ibm.com/epubs/pdf/a227832d.pdf
+(3) Collection of z/Architecture publications
+    https://linux.mainframe.blog/zarchitecture-principles-of-operation/