Update incorrect docs about scheduler window ids (#6781)

Updates the drmemtrace scheduler regions_of_interest docs which
incorrectly stated the window id markers were not inserted between
back-to-back regions: they are inserted, as the code confirms (with an
explicit comment) and the unit tests check.

clients/drcachesim/scheduler/scheduler.h

@@ -220,10 +220,10 @@ template <typename RecordType, typename ReaderType> class scheduler_tmpl_t {
  * though the input were constructed by concatenating these ranges together. A
  * #TRACE_MARKER_TYPE_WINDOW_ID marker is inserted between
  * ranges (with a value equal to the range ordinal) to notify the client of the
- * discontinuity (but not before the first range nor between back-to-back regions
- * with no separation), with a #dynamorio::drmemtrace::TRACE_TYPE_THREAD_EXIT
- * record inserted after the final range. These ranges must be non-overlapping
- * and in increasing order.
+ * discontinuity. This marker is inserted between back-to-back regions with no
+ * separation, but it is not inserted prior to the first range. A
+ * #dynamorio::drmemtrace::TRACE_TYPE_THREAD_EXIT record is inserted after the
+ * final range. These ranges must be non-overlapping and in increasing order.
  */
  std::vector<range_t> regions_of_interest;
  };