docs: add sha256 checksums for 13.0.6

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
diff --git a/docs/relnotes/13.0.6.html b/docs/relnotes/13.0.6.html
index 13464dd..9183fc4 100644
--- a/docs/relnotes/13.0.6.html
+++ b/docs/relnotes/13.0.6.html
@@ -31,7 +31,8 @@
 
 <h2>SHA256 checksums</h2>
 <pre>
-TBD
+1076590f29103f022a2cd87e6dff6ae77072013745603d06b0410c373ab2bb1a  mesa-13.0.6.tar.gz
+29ef104a7fc082d352b1599bd6cb1d040be424ccd22f5e0eb7ee9b0e9acd3597  mesa-13.0.6.tar.xz
 </pre>