client: manifest: archlinux: finance: add "related" category

Describes packages/commands that are "related" but not dependencies.

client/docker-finance.yaml

@@ -48,6 +48,11 @@ container:
           - "hledger-iadd --version"
           - "hledger-ui --version"
           - "hledger-web --version"
+      related:
+        packages:
+          - "calc"
+          - "less"
+        commands:
       fetch:
         packages:
           - "composer"