Merge pull request #536 from oasisprotocol/amela/testnet-upgrade-23.0…

…-ubuntu-info

docs/node/testnet: Add notice about prebuild binaries

docs/node/testnet/upgrade-log.md

@@ -67,6 +67,14 @@ an updated ParaTime containing new trust roots is released and adopted.
 
 7. Replace the old version of Oasis Node with version [23.0].
 
+:::info
+
+The Oasis Core 23.0 binary in our published releases is built only for Ubuntu
+22.04. You'll have to build it yourself if you're using prior Ubuntu versions
+(or other distributions using older system libraries).
+
+:::
+
 8. Perform any needed [configuration changes](#configuration-changes) described
    below.