Bonus: boilerplate to put in project’s README

Nice way of introducing dependency management process to new team members for copy-pasting to README.md:

## Dependency management

This project uses [pip-compile-multi](https://pypi.org/project/pip-compile-multi/) for hard-pinning dependencies versions.
Please see its documentation for usage instructions.
In short, `requirements/base.in` contains the list of direct requirements with occasional version constraints (like `Django<2`)
and `requirements/base.txt` is automatically generated from it by adding recursive tree of dependencies with fixed versions.
The same goes for `test` and `dev`.

To upgrade dependency versions, run `pip-compile-multi`.

To add a new dependency without upgrade, add it to `requirements/base.in` and run `pip-compile-multi --no-upgrade`.

For installation always use `.txt` files. For example, command `pip install -Ue . -r requirements/dev.txt` will install
this project in development mode, testing requirements and development tools.
Another useful command is `pip-sync requirements/dev.txt`, it uninstalls packages from your virtualenv that aren't listed in the file.