修改IoTDB的文档。

src/HealthChecks.IoTDB/README.md

-# Cassandra Health Check
+# IoTDB Health Check
 
-This health check verifies the ability to communicate with a Cassandra server.
+This health check verifies the ability to communicate with a IoTDB server.
 
 ## Example Usage
 
 With all of the following examples, you can additionally add the following parameters:
 
-- `name`: The health check name. Default if not specified is `Cassandra`.
+- `name`: The health check name. Default if not specified is `IoTDB`.
 - `failureStatus`: The `HealthStatus` that should be reported when the health check fails. Default is `HealthStatus.Unhealthy`.
 - `tags`: A list of tags that can be used to filter sets of health checks.
 - `timeout`: A `System.TimeSpan` representing the timeout of the check.
 
 ### Basic
 
-This will create a new `CassandraClient` and reuse it on every request to get the health check result. Use
-the extension method where you provide the `Uri` to connect with. 
+This will create a new `SessionPool` and reuse it on every request to get the health check result. Use
+the extension method where you provide the `connectionString` to connect with. 
 
 ```csharp
   public void ConfigureServices(IServiceCollection services)
    {
     services.AddHealthChecks()
-      .AddCassandra("");
+      .AddIoTDB("");
     }
 ```
 
@@ -30,11 +30,8 @@ you must ensure automatic recovery is enabled so that the `CassandraClient` can
 ```csharp
     public void ConfigureServices(IServiceCollection services)
     {
-      services.AddSingleton<CassandraClient>(sp =>  Cluster.Builder()
-        .AddContactPoint("127.0.0.1")
-        .WithGraphOptions(new GraphOptions().SetName("demo"))
-        .Build())
+      services.AddSingleton<SessionPool>(sp =>   new SessionPool(connectionString))
       .AddHealthChecks()
-      .AddCassandra();
+      .AddIoTDB();
     }
 ```