docs: update calendar, add news and link release notes to 18.0.3

Signed-off-by: Juan A. Suarez Romero <jasuarez@igalia.com>
diff --git a/docs/relnotes.html b/docs/relnotes.html
index 2b762bf..78af393 100644
--- a/docs/relnotes.html
+++ b/docs/relnotes.html
@@ -21,6 +21,7 @@
 </p>
 
 <ul>
+<li><a href="relnotes/18.0.3.html">18.0.3 release notes</a>
 <li><a href="relnotes/18.0.2.html">18.0.2 release notes</a>
 <li><a href="relnotes/18.0.1.html">18.0.1 release notes</a>
 <li><a href="relnotes/17.3.9.html">17.3.9 release notes</a>