pd: add note for member leader_priority (pingcap#19165)

Author: qiancai

dr-multi-replica.md

@@ -122,7 +122,7 @@ In this example, TiDB contains five replicas and three regions. Region 1 is the
 
     > **Note:**
     >
-    > The greater the priority number, the higher the probability that this node becomes the leader.
+    > In all available PD nodes, the node with the highest priority number becomes the leader.
 
 3. Create placement rules and fix the primary replica of the test table to region 1:
 

pd-control.md

@@ -471,6 +471,20 @@ Success!
 ......
 ```
 
+Specify the priority of PD leader:
+
+```bash
+member leader_priority  pd-1 4
+member leader_priority  pd-2 3
+member leader_priority  pd-3 2
+member leader_priority  pd-4 1
+member leader_priority  pd-5 0
+```
+
+> **Note:**
+>
+> In all available PD nodes, the node with the highest priority number becomes the leader.
+
 ### `operator [check | show | add | remove]`
 
 Use this command to view and control the scheduling operation.

placement-rules-in-sql.md

@@ -409,7 +409,7 @@ You can specify a specific distribution of Leaders and Followers using constrain
 If you have specific requirements for the distribution of Raft Leaders among nodes, you can specify the placement policy using the following statement:
 
 ```sql
-CREATE PLACEMENT POLICY deploy221_primary_east1 LEADER_CONSTRAINTS="[+region=us-east-1]" FOLLOWER_CONSTRAINTS='{"+region=us-east-1": 1, "+region=us-east-2": 2, "+region=us-west-1: 1}';
+CREATE PLACEMENT POLICY deploy221_primary_east1 LEADER_CONSTRAINTS="[+region=us-east-1]" FOLLOWER_CONSTRAINTS='{"+region=us-east-1": 1, "+region=us-east-2": 2, "+region=us-west-1": 1}';
 ```
 
 After this placement policy is created and attached to the desired data, the Raft Leader replicas of the data will be placed in the `us-east-1` region specified by the `LEADER_CONSTRAINTS` option, while other replicas of the data will be placed in regions specified by the `FOLLOWER_CONSTRAINTS` option. Note that if the cluster fails, such as a node outage in the `us-east-1` region, a new Leader will still be elected from other regions, even if these regions are specified in `FOLLOWER_CONSTRAINTS`. In other words, ensuring service availability takes the highest priority.

three-data-centers-in-two-cities-deployment.md

@@ -197,7 +197,7 @@ In the deployment of three AZs in two regions, to optimize performance, you need
    >
    > Starting from TiDB v5.2, the `label-property` configuration is not supported by default. To set the replica policy, use the [placement rules](/configure-placement-rules.md).
 
-- Configure the priority of PD. To avoid the situation where the PD leader is in another region (AZ3), you can increase the priority of local PD (in Seattle) and decrease the priority of PD in another region (San Francisco). The larger the number, the higher the priority.
+- Configure the priority of PD. To avoid the situation where the PD leader is in another region (AZ3), you can increase the priority of local PD (in Seattle) and decrease the priority of PD in another region (San Francisco). The larger the number, the higher the priority. In all available PD nodes, the node with the highest priority number becomes the leader.
 
     ```bash
     member leader_priority PD-10 5