update readme

Download link：

For java: https://github.com/NewbieOrange/SUSTech-SQL-Project2-Public

For python: https://github.com/ziqin/SUSTech-CS307-Project2-Python

https://mirrors.sustech.edu.cn/git/sustech-2021fall-db/sustech-sql-project

### Interface Specification

### Tips

Please create database with `UTF8` encoding and `en_US.UTF8` locale, or you may encounter ordering bugs.

Please create database with `C` encoding and `C` locale, or you may encounter ordering bugs.

See: https://github.com/NewbieOrange/SUSTech-SQL-Project2-Public/issues/88

- Your implementation should throw `java.lang.UnsupportedOperationException` if a method is not actually implemented,

  so the tests can fail quickly.

#### Python

- All `add*()` functions with return value of int should return the (presumably auto-generated) ID.

- All arguments are guaranteed to follow the type hints. Arguments passed won't be `None` unless explicitly annotated

  with `Optional`.

- For return types with type hints, return values (and their fields) should not be `None`, unless explicitly documented.

  Use `[]`, `{}`, `set()` or their equivalents instead of `None` for empty container in return values.

- Your implementation should raise `NotImplementedError` if a method is not actually implemented, so that tests can

  fail quickly.

### Rules

- In this project, we use Maven to manage dependent libraries. If you want to introduce a new library, you need to

  record it in `pom.xml`. Your dependencies should be downloadable from the Maven Central repository.

#### Python-specific rules

TO BE ADDED

## 2. What to submit?

- The jar file built using maven-assembly (Run `IDEA-Maven-Plugins-assembly-single`)

  in `/target/xxxx-with-dependencies.jar`.

### If you are using Python:

## 3. What to deliver?

### Project Timeline

Code Submission Deadline: **June 6th**

Code Submission Deadline: **December 31th**

Presentation Time: **June 15th** by Tencent Meeting

Presentation Time: **December 31th** in Lab class