[DOC] Fix the description of rb_path_check

c.f. #20971

Author: nobu

include/ruby/internal/intern/hash.h

@@ -287,12 +287,15 @@ VALUE rb_hash_update_by(VALUE hash1, VALUE hash2, rb_hash_update_func *func);
 /* file.c */
 
 /**
- * This function is mysterious.  What it does is not immediately obvious.  Also
- * what it does seems platform dependent.
+ * If the PATH_SEPARATOR-separated list of directory names contains the name of
+ * a world-writable directory, issue a warning  for it.  This may do nothing on
+ * some platforms.
  *
  * @param[in]  path       A local path.
  * @retval     0          The "check" succeeded.
  * @retval     otherwise  The "check" failed.
+ * @note       This  feature may  be  disabled  by setting  `ENABLE_PATH_CHECK`
+ *             macro to zero at compilation time.
  */
 int rb_path_check(const char *path);