Run pre-commit install inside the environment (#525)

We shouldn't encourage the user to install it separately. This should be (and is) handled by the `environment.yml`.

docs/contributing.rst

@@ -31,29 +31,30 @@ Install for development
 --------------------------------------------------
 
 The first step is to set up a conda environment and install glum in editable mode.
+We strongly suggest to use ``mamba`` instead of ``conda`` as this provides the same functionality at much greater speed.
+
 ::
 
    # First, make sure you have conda-forge as your primary conda channel:
    conda config --add channels conda-forge
 
-   # And install pre-commit
-   conda install -y pre-commit
-
    # Clone the repository
    git clone git@github.com:Quantco/glum.git
    cd glum
 
-   # Set up our pre-commit hooks for black, mypy, isort and flake8.
-   pre-commit install
-
    # Set up a conda environment with name "glum"
-   conda env create
+   mamba env create
 
    # If you want to install the dependencies necessary for benchmarking against other GLM packages:
-   conda env update -n glum --file environment-benchmark.yml
+   mamba env update -n glum --file environment-benchmark.yml
 
-   # Install this package in editable mode. 
+   # Activate the previously created conda environment
    conda activate glum
+
+   # Set up our pre-commit hooks for black, mypy, isort and flake8.
+   pre-commit install
+
+   # Install this package in editable mode.
    pip install --no-use-pep517 --disable-pip-version-check -e .