Merge upstream master and move the reveal docs into docs/

Upstream moved the documentation sources from doc/ to docs/ (#7584), so the
page this branch adds now belongs under docs/doxygen/pages/user_documentation/
gameplay/. The index.md edit auto-merged onto the moved file, but the new page
stayed at the old path, and GitHub's merge engine reported a conflict in
index.md because the file it edits was deleted upstream.

No source changes: the merge is upstream/master as-is plus the doc relocation.

docs/doxygen/pages/user_documentation/index.md

@@ -0,0 +1,34 @@
+@page user_reference User Reference
+
+## Deck Management
+
+- @subpage creating_decks
+- @subpage importing_decks
+- @subpage editing_decks
+- @subpage exporting_decks
+
+## Gameplay
+
+- @subpage revealing_cards
+
+## Release Channels
+
+- @subpage beta_release
+
+## Settings
+
+- @subpage settings_folder
+
+## Card Pictures
+
+- @subpage custom_card_pictures
+
+## Troubleshooting
+
+- @subpage fixing_card_pictures
+- @subpage enabling_debug_logs
+
+## Syntax Help
+
+- @subpage search_syntax_help
+- @subpage deck_search_syntax_help