docs: declare where the data comes from, and under what terms

The module's own Apache-2.0 licence covers its code and says nothing
about the material it fetches. STORE.yaml now carries a data_source
block (publisher, url, terms, required attribution, and bundled:
false), and MODULE.md/MODULE.de.md explain it in both languages,
including the sentence that the retrieved text does not replace the
official version.

Enforced platform-side by data_source_gap in chain_hub::store_index;
the four rules are written up in docs/architecture/store-format.md of
the platform repo.

Signed-off-by: flemming-it <sf@flemming.it>

STORE.yaml

@@ -7,6 +7,17 @@ author:
 
 license: Apache-2.0
 
+# Where the data comes from, and under what terms. The `license`
+# above covers this module's code; this block covers the material
+# the module reaches. See docs/architecture/store-format.md.
+data_source:
+  name: "gesetze-im-internet.de (BMJ / juris GmbH)"
+  url: https://www.gesetze-im-internet.de/
+  license: "Amtliches Werk (§ 5 UrhG), gemeinfrei"
+  attribution: "Quelle: gesetze-im-internet.de (Bundesministerium der Justiz)"
+  # Never true: the module fetches at runtime and ships no corpus.
+  bundled: false
+
 tagline:
   en: "Fetch German federal law from gesetze-im-internet.de"
   de: "Deutsches Bundesrecht von gesetze-im-internet.de holen"