added standards.md

## CSST L1 Pipeline Standards

### Workplace

Gitlab Group **CSST-L1**:

https://csst-tb.bao.ac.cn/code/csst-l1

### Prototype

https://csst-tb.bao.ac.cn/code/csst-l1/csst_proto

### Structure of files

An example of the tree

```bash

csst_proto

 |-csst_proto

 |  |-data

 |  |  |-test_image.txt

 |  |  |-table_data.txt

 |  |-__init__.py

 |  |-flip_image.py

 |  |-some_other_modules.py

 |  |-top_level_interface.py

 |-tests

 |-doc (sphinx directory)

 |-setup.py

 |-LICENSE

 |-README.md

```

1. `setup.py`

    this file 

2.

### Code style

PEP8.

### Documentation

sphinx-based documentation needs docstrings.

1. docstring styles

    - Numpy (recommended)

    - Google

### Unit Tests