📝 Instructions for upgrading Java and Node.js versions

Why:
- It's more than just one command with asdf. Considered writing a script
  for it, but it's not that complicated, after all.
- For Java, we need to specify the LTS version. The versions are easier
  to keep in sync when there is a command to copy-paste.
- Added the command for setting also the global version, since that's
  typically what we want to do after upgrading to the latest version.

README.md

@@ -77,6 +77,14 @@ Upgrade dependencies
     lein ancient upgrade :all :check-clojure :no-tests
     npm run upgrade
 
+    asdf install java latest:temurin-21
+    asdf local java latest:temurin-21
+    asdf global java latest:temurin-21
+
+    asdf install nodejs latest
+    asdf local nodejs latest
+    asdf global nodejs latest
+
 Download dependency sources
 
     lein pom