Cleanup: clarify and update some flags descriptions in libquery code.

source/blender/blenkernel/BKE_lib_query.h

@@ -71,11 +71,15 @@ enum {
   IDWALK_CB_OVERRIDE_LIBRARY_REFERENCE = (1 << 5),
 
   /**
-   * Adjusts #ID.us reference-count.
-   * \note keep in sync with 'newlibadr_us' use in readfile.c
+   * This ID usage is fully refcounted.
+   * Callback is responsible to deal accordingly with #ID.us if needed.
    */
   IDWALK_CB_USER = (1 << 8),
-  /** Ensure #ID.us is at least 1 on use. */
+  /**
+   * This ID usage is not refcounted, but at least one user should be generated by it (to avoid
+   * e.g. loosing the used ID on save/reload).
+   * Callback is responsible to deal accordingly with #ID.us if needed.
+   */
   IDWALK_CB_USER_ONE = (1 << 9),
 };