docs: add CONTIRBUTING.md installation of basic dependencies for Python

[daipom]

What feature or improvement would you like to see?

arrow-adbc/CONTRIBUTING.md

Lines 366 to 373 in 8a300e1

	Python libraries are managed with [setuptools][setuptools]. See
	individual READMEs for additional dependencies. In general, that
	means all projects can be built as follows:
	```shell
	$ cd python/adbc_driver_manager
	$ pip install -e .
	```

It would be helpful to add this command.

$ mamba install --file ci/conda_env_python.txt

[daipom]

take