describe how to use taosdemo in readme.md

tests/examples/JDBC/taosdemo/readme.md

-
+```
+cd tests/examples/JDBC/taosdemo
+mvn clean package -Dmaven.test.skip=true
+# 先建表，再插入的
+java -jar target/taosdemo-2.0-jar-with-dependencies.jar -host [hostname] -database [database] -doCreateTable true -superTableSQL "create table weather(ts timestamp, f1 int) tags(t1 nchar(4))" -numOfTables 1000 -numOfRowsPerTable 100000000 -numOfThreadsForInsert 10 -numOfTablesPerSQL 10 -numOfValuesPerSQL 100
+# 不建表，直接插入的
+java -jar target/taosdemo-2.0-jar-with-dependencies.jar -host [hostname] -database [database] -doCreateTable false -superTableSQL "create table weather(ts timestamp, f1 int) tags(t1 nchar(4))" -numOfTables 1000 -numOfRowsPerTable 100000000 -numOfThreadsForInsert 10 -numOfTablesPerSQL 10 -numOfValuesPerSQL 100
+```
 
 需求：
 1. 可以读lowa的配置文件