Fix description about hot-region-cache-hits-threshold (#5721) (#5722)

pd-control.md

@@ -271,7 +271,7 @@ Usage:
     >> config set hot-region-schedule-limit 4       // 4 tasks of hot Region scheduling at the same time at most
     ```
 
-- `hot-region-cache-hits-threshold` is used to set the threshold of a hot Region. A Region is considered as hot only if the number of its cache hits exceeds this threshold.
+- `hot-region-cache-hits-threshold` is used to set the number of minutes required to identify a hot Region. PD can participate in the hotspot scheduling only after the Region is in the hotspot state for more than this number of minutes.
 
 - `tolerant-size-ratio` controls the size of the balance buffer area. When the score difference between the leader or Region of the two stores is less than specified multiple times of the Region size, it is considered in balance by PD.