Credit BepInEx/UnityExplorer, fix stale README refs

BepInEx install/uninstall verified end-to-end against a scratch game dir:
installs loader + plugin, uninstall removes both and leaves BepInEx/ intact.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

THIRD_PARTY.md

@@ -17,6 +17,21 @@ them; all runtime patching is performed by SUWSF.
 - License: MIT
 - Files: `vendor/SUWSF-x64/dsound.dll` (renamed proxy; adapts by filename)
 
+## BepInEx
+- Author: BepInEx contributors
+- Source: https://github.com/BepInEx/BepInEx
+- License: LGPL-2.1
+- Files: `vendor/BepInEx_win_x64_5.4.23.5.zip` (redistributed unmodified)
+- Used by Unity games (e.g. Burglin' Gnomes) to load the C# fix plugin.
+
+## UnityExplorer (development only)
+- Author: sinai-dev
+- Source: https://github.com/sinai-dev/UnityExplorer
+- License: GPL-3.0
+- Files: `vendor/UnityExplorer.BepInEx5.Mono.zip`
+- Used only for runtime inspection while developing a fix; it is NOT part of any
+  release package and is not required by end users.
+
 ## Patch patterns
 The `AspectRatioAxisConstraint` (HOR+) and `ConstrainAspectRatio` (pillarbox)
 byte patterns in `games/*/SUWSF.ini` are adapted from the UE4 fixes in