Docs: note the purpose of UserDef_Runtime.is_dirty

source/blender/makesdna/DNA_userdef_types.h

@@ -589,6 +589,7 @@ typedef struct WalkNavigation {
 } WalkNavigation;
 
 typedef struct UserDef_Runtime {
+  /** Mark as changed so the preferences are saved on exit. */
   char is_dirty;
   char _pad0[7];
 } UserDef_Runtime;

source/blender/makesrna/intern/rna_userdef.c

@@ -217,9 +217,10 @@ static void rna_userdef_version_get(PointerRNA *ptr, int *value)
   value[2] = userdef->subversionfile;
 }
 
+/** Mark the preferences as being changed so they are saved on exit. */
 #  define USERDEF_TAG_DIRTY rna_userdef_is_dirty_update_impl()
 
-/* Use single function so we can more easily breakpoint it. */
+/** Use single function so we can more easily break-point it. */
 void rna_userdef_is_dirty_update_impl(void)
 {
   /* We can't use 'ptr->data' because this update function