Add instructions to install extra dependencies with poetry (#2686)

* add poetry install -e instruction

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* make new section

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* Update docs/source/contributing/development.rst

Co-authored-by: Benjamin Hackl <[email protected]>

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Benjamin Hackl <[email protected]>

Author: 3 people

docs/source/contributing/development.rst

@@ -66,6 +66,10 @@ For first-time contributors
      as create and enter a virtual environment. You can always re-enter
      that environment by running ``poetry shell``.
 
+   - In case you want to install extra dependencies that are defined in
+     the ``[tool.poetry.extras]``  section of ``pyproject.toml``, this can be done by passing
+     the ``-E`` flag, for example ``poetry install -E jupyterlab -E gui``.
+
    - In case you decided against Poetry, you can install Manim via pip
      by running ``python3 -m pip install .``. Note that due to our
      development infrastructure being based on Poetry, we currently