docs: Update release calendar, add news item, and add release notes for 18.1.5
diff --git a/docs/relnotes.html b/docs/relnotes.html
index eecb5a8..9d4a262 100644
--- a/docs/relnotes.html
+++ b/docs/relnotes.html
@@ -21,6 +21,7 @@
 </p>
 
 <ul>
+<li><a href="relnotes/18.1.5.html">18.1.5 release notes</a>
 <li><a href="relnotes/18.1.4.html">18.1.4 release notes</a>
 <li><a href="relnotes/18.1.3.html">18.1.3 release notes</a>
 <li><a href="relnotes/18.1.2.html">18.1.2 release notes</a>