docs: Add release notes for v5.1.0a1

DIRACGrid CI · DIRACGrid CI · commit c656aeb3994b · 2022-09-29T08:28:57.000Z
diff --git a/release.notes b/release.notes
@@ -1,3 +1,4 @@
+[v5.1.0a1]
 [v5.0.0]
 [v5.0.0a22]
 
