Update readme

Signed-off-by: junjie.jiang <junjie.jiang@zilliz.com>

README.md

@@ -31,7 +31,7 @@ for data in DataLoader(ops.data_source.sql('sqlite:///./sqlite.db')):
     print(p(data).to_list(kv_format=True))
 
 # batch
-for data in DataLoader(ops.data_source.glob('sqlite:///./sqlite.db'), batch_size=10):
+for data in DataLoader(ops.data_source.sql('sqlite:///./sqlite.db'), batch_size=10):
     p.batch(data)
 ```
 
@@ -62,7 +62,7 @@ If you want to query specific columns, use the column names and separate them wi
 
 Where conditional statement, for example: id > 100
 
-***limit:* *int*
+***limit:*** *int*
 
 The default value is 500. If set to None, all data will be returned.