Docs: Add & link xsd schema information (#6439)

* Add xsd scheme information

* further references as list

doc/doxygen/extra-pages/developer_documentation/card_database_schema_and_parsing.md

@@ -1,3 +1,16 @@
 @page card_database_schema_and_parsing Card Database Schema and Parsing
 
+# Card Database Schemas
+
+Cockatrice uses `XML files` to store information of available cards to be used in the app (`cards.xml`).  
+The token file follows the schema of the card database (`tokens.xml`), too.
+
+Saved decks (`<deckname>.xml`) use a different schema.
+
+- [XSD Schema for `Card Databases`](https://github.com/Cockatrice/Cockatrice/blob/master/doc/carddatabase_v4/cards.xsd) <kbd>v4</kbd>
+- [XSD Schema for `Decks`](https://github.com/Cockatrice/Cockatrice/blob/master/doc/deck.xsd) <kbd>v1</kbd>
+
+
+# Card Database Parsing
+
 TODO

doc/doxygen/extra-pages/user_documentation/deck_management/creating_decks.md

@@ -8,10 +8,8 @@ by selecting "Deck Editor" or "Visual Deck Editor" under the "Tabs" application
 
 # Further References
 
-See @ref editing_decks for information on how to modify the attributes and contents of a deck in the Deck Editor
+- See @ref editing_decks for information on how to modify the attributes and contents of a deck in the Deck Editor
 widgets.
-
-See @ref exporting_decks for information on how to store and persist your deck either in-client or to external
+- See @ref exporting_decks for information on how to store and persist your deck either in-client or to external
 services.
-
-See @ref importing_decks for information on how to import existing decks either in-client or from external services
+- See @ref importing_decks for information on how to import existing decks either in-client or from external services