Add developer's guide in the readme.

README.md

@@ -16,3 +16,39 @@ cp resources/config.sample.json config.20240405.json
 ```
 
 Then ``scicat_ingestor`` will automatically use the configuration file.
+
+## Developer's Guide
+
+### Virtual Environments
+We use [pip-compile-multi](https://pip-compile-multi.readthedocs.io/en/latest/) to maintain
+the `pip` recipes under `requirements`.
+Each `*.in` files have the dependencies for specific purposes and `*.txt` files are compiled frozen dependencies.
+`base.in` is auto-generated by `make_base.py` script based on `pyproject.toml`,
+but you can add/pin dependencies manually above the marker in the file.
+
+We use [tox](#Tox) command, `tox -e deps` to freeze the dependencies.
+
+### Pre-commit Hooks
+We use `pre-commit` for formatting and static analysis of the code.
+Once you clone the repository and set up the virtual environment (i.e. installed `requirements/dev.txt`)
+you need to install [pre-commit](https://pre-commit.com/index.html) by
+```bash
+pre-commit install
+```
+`pre-commit` will be hooked whenever you make a `git commit` and screen the files of interest.
+
+It will not pass CI test if `pre-commit` complains.
+If you want to push the change while having a PR open, even if you know that `pre-commit hooks` fail,
+you can add `[ci-skip]` tag in your commit and CI action will be skipped.
+
+### Copier Template
+This repository was based on [scipp/copier_template](https://github.com/scipp/copier_template).
+We can apply common updates/dependency updates using
+```bash
+copier update
+```
+
+### Tox
+`tox` controls virtual environment and commands for various purposes.
+Developers and CI actions can use the command.
+For example, `tox -e docs` builds documentation under `./html` directory and `tox -e py310` will run unit tests with python version `3.10`.