docs: add changelog entry for updates since v0.6c

changelog.txt

@@ -1,5 +1,38 @@
 !!! --- Q3Rally Changelog --- !!!
 
+new since v0.6c
+
+Added:
+
+- New in-game HUD Elements menu (Shift+H) with per-element toggles
+- New Content Manager download system in the UI
+- New Advanced Graphics menu with presets, sun shadow controls and more rendering options
+- New hybrid waypoint system for racing bots (ghost source + flexible steering)
+- Added staged damage support for func_breakable objects
+- Added/updated NetRadiant GamePack data
+- Added bilingual atmospheric mapper guide (DE/EN)
+
+Improved:
+
+- Controller support across menus, bindings and loading flow
+- Q3R Options menu cleaned up and reorganized into a clearer two-column layout
+- Controls UX improved with racing defaults, search and mapper/dev bindings
+- Profile flow moved into the main menu with a lighter create/select overlay
+- Racing and Elimination flow robustness, HUD feedback and race UX
+- Vehicle handling CVars now replicated/latched for better server-client consistency
+- CI/build and Flatpak metadata updates
+
+Fixed:
+
+- Main menu no longer shows the GFX loading screen again after first launch
+- Credits screen merge/rewrite and scroll behavior fixes
+- UI hitboxes for CHANGE PLATE and Downloads tabs
+- Race-observer fallback crash in follow mode
+- Anisotropy menu selection and Driver Info spacing issues
+- Race grid spawn fallback now avoids defaulting to DM spawns
+- Derby damage CVar validation and collision/ram damage rebalance
+- Ridge Racer map fix plus missing texture/file cleanup
+
 new in v0.5
 
 Fixed:
@@ -114,4 +147,4 @@ Fixed:
 – q3r_ctf_01 updated
 – shotgun bullet bug fixed
 – fixed bug in bot path creation system
-– reworked readme files
+– reworked readme files