doc: fix the example

Author: jackwener

README.md

@@ -44,23 +44,19 @@ Successfully installed tikv-client-0.1.0
 Python TiKV client is synchronous by defult:
 
 ```python
-from tikv_client import TransactionClient
+from tikv_client import RawClient
 
-client = TransactionClient.connect("127.0.0.1:2379")
+client = RawClient.connect(["127.0.0.1:2379"])
 
-txn = client.begin(pessimistic=True)
-txn.put(b"k1", b"v1")
-txn.put(b"k2", b"v2")
-txn.put(b"k3", b"v3")
-txn.put(b"k4", b"v4")
-txn.put(b"k5", b"v5")
-txn.commit()
+client.put(b"k1", b"v1")
+client.put(b"k2", b"v2")
+client.put(b"k3", b"v3")
+client.batch_put({b"k4": b"v4", b"k5": b"v5"})
 
-snapshot = client.snapshot(client.current_timestamp())
-print(snapshot.get(b"k3"))
-print(snapshot.batch_get([b"k1", b"k4"]))
+print(client.get(b"k3"))
+print(client.batch_get([b"k1", b"k4"]))
 
-for k, v in snapshot.scan(b"k1", end=None, limit=10, include_start=False):
+for k, v in client.scan(b"k1", end=None, limit=10, include_start=False):
     print(k, v)
 ```
 
@@ -71,7 +67,7 @@ import asyncio
 from tikv_client.asynchronous import TransactionClient
 
 async def main():
-    client = await TransactionClient.connect("127.0.0.1:2379")
+    client = await TransactionClient.connect(["127.0.0.1:2379"])
 
     txn = await client.begin(pessimistic=True)
     await txn.put(b"k1", b"v1")
@@ -81,7 +77,7 @@ async def main():
     await txn.put(b"k5", b"v5")
     await txn.commit()
 
-    snapshot = client.snapshot(await client.current_timestamp())
+    snapshot = client.snapshot(await client.current_timestamp(), pessimistic=True)
     print(await snapshot.get(b"k3"))
     print(await snapshot.batch_get([b"k1", b"k4"]))