docs: clean up field usage

We currently have a mixture of several fields in our package docs. Between historic patterns and new workflows, each package may feature one or more of:

1. comment - a generic field for providing commentary on a package. This was previously always used to provide a link to a GPL sources tarball if required for a package
2. warning - usually used to indicate we've had to skip some sort of test or omit a piece of functionality in a module, due to incompatibility or known issues with riscv64 or our infrastructure
3. patched - a typically blank field used to signal that the package is built with one or more patches applied during the process

These are all somewhat redundant. I propose two to replace these:

1. gpl-sources - specify this with one or more links if we have to provide GPL source tarballs as part of the package builds
2. comment - anything else (notes about patching, skipping tests, etc.) goes here

@justeph @luhenry thoughts?

Das Issue nennt keine spezifischen Dateien oder Tests; finde zunächst die Felder in der Paketdokumentation, die derzeit comment, warning und patched verwenden. Bestätige das vorgeschlagene Feldschema, bevor du Einträge migrierst: Verwende gpl-sources für GPL-Quelllinks und comment für andere Hinweise; überprüfe anschließend, dass keine Verwendung alter Felder mehr vorhanden ist.