docs: add sha256 checksums for 18.0.5

Signed-off-by: Juan A. Suarez Romero <jasuarez@igalia.com>
diff --git a/docs/relnotes/18.0.5.html b/docs/relnotes/18.0.5.html
index 03b33c8..6ae66c7 100644
--- a/docs/relnotes/18.0.5.html
+++ b/docs/relnotes/18.0.5.html
@@ -31,7 +31,8 @@
 
 <h2>SHA256 checksums</h2>
 <pre>
-TBD
+ea3e00329cea899b1e32db812fd2f426832be37e4baa2e2fd9288a3480f30531  mesa-18.0.5.tar.gz
+5187bba8d72aea78f2062d134ec6079a508e8216062dce9ec9048b5eb2c4fc6b  mesa-18.0.5.tar.xz
 </pre>