docs: Add sha256 sums for the 10.4.7 release

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>

docs/relnotes/10.4.7.html

@@ -30,7 +30,9 @@ because compatibility contexts are not supported.
 
 <h2>SHA256 checksums</h2>
 <pre>
-TBD
+9e7b59267199658808f8b33e0410b86fbafbdcd52378658b9df65fac9d24947f  MesaLib-10.4.7.tar.gz
+2c351c98671f9a7ab3fd9c601bb7a255801b1580f5dd0992639f99152801b0d2  MesaLib-10.4.7.tar.bz2
+d14ac578b5ce16560757b53fbd1cb4d6b34652f8e110e4b10a019adc82e67ffd  MesaLib-10.4.7.zip
 </pre>
 
 <h2>New features</h2>