Add instruction to install Box2D header files. [ci skip]

Source/CMake/Modules/FindUrho3D.cmake

@@ -130,7 +130,7 @@ else ()
 
     if (URHO3D_INCLUDE_DIRS)
         set (BASE_DIR ${URHO3D_INCLUDE_DIRS})
-        set (DIRS Box2D Bullet kNet SDL)
+        set (DIRS Bullet kNet SDL)
         if (ENABLE_ANGELSCRIPT)
             list (APPEND DIRS AngelScript)
         endif ()

Source/ThirdParty/Box2D/CMakeLists.txt

@@ -157,6 +157,9 @@ source_group(Dynamics\\Joints FILES ${BOX2D_Joints_SRCS} ${BOX2D_Joints_HDRS})
 source_group(Include FILES ${BOX2D_General_HDRS})
 source_group(Rope FILES ${BOX2D_Rope_SRCS} ${BOX2D_Rope_HDRS})
 
+# Install dependency for Engine/Urho2D/PhysicsWorld2D.h and Engine/Urho2D/RigidBody2D.h
+install (DIRECTORY Box2D DESTINATION ${DEST_INCLUDE_DIR} USE_SOURCE_PERMISSIONS FILES_MATCHING PATTERN *.h)
+
 # Define dependency libs
 set (INCLUDE_DIRS_ONLY .)