updated installing instructions to use pip

[tkknight]

🚀 Pull Request

Description

Updated the installing instructions to use:

pip install --no-deps --editable .

instead of:

python setup.py develop

Using pip is considered better practice, also the old way shows a couple of strong warnings:

/home/theuser/projects/iris
$ python setup.py develop
/home/theuser/.conda/envs/iris-dev/lib/python3.11/site-packages/setuptools/config/pyprojecttoml.py:66: _BetaConfiguration: Support for [tool.setuptools] in pyproject.toml is still *beta*.
  config = read_configuration(filepath, True, ignore_option_errors, dist)
running develop
/home/theuser/.conda/envs/iris-dev/lib/python3.11/site-packages/setuptools/command/develop.py:40: EasyInstallDeprecationWarning: easy_install command is deprecated.
!!

        ********************************************************************************
        Please avoid running ``setup.py`` and ``easy_install``.
        Instead, use pypa/build, pypa/installer, pypa/build or
        other standards-based tools.

        See https://github.com/pypa/setuptools/issues/917 for details.
        ********************************************************************************

!!
  easy_install.initialize_options(self)
/home/theuser/.conda/envs/iris-dev/lib/python3.11/site-packages/setuptools/_distutils/cmd.py:66: SetuptoolsDeprecationWarning: setup.py install is deprecated.
!!

        ********************************************************************************
        Please avoid running ``setup.py`` directly.
        Instead, use pypa/build, pypa/installer, pypa/build or
        other standards-based tools.

        See https://blog.ganssle.io/articles/2021/10/setup-py-deprecated.html for details.
        ********************************************************************************

!!
  self.initialize_options()
running egg_info
writing lib/scitools_iris.egg-info/PKG-INFO
writing dependency_links to lib/scitools_iris.egg-info/dependency_links.txt
writing requirements to lib/scitools_iris.egg-info/requires.txt
writing top-level names to lib/scitools_iris.egg-info/top_level.txt
reading manifest template 'MANIFEST.in'
<SNIP>

---

Consult Iris pull request check list

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (6cecf04) 89.32% compared to head (58fa0dd) 89.32%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5273   +/-   ##
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  Coverage   89.32%   89.32%           
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  Files          89       89           
  Lines       22390    22390           
  Branches     5374     5374           
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  Hits        20000    20000           
  Misses       1640     1640           
  Partials      750      750           

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[trexfeathers]

Thanks @tkknight! Is there more to do on this (still in Draft)?

[bjlittle]

@tkknight Lovely change 👍

Thanks for showing the docs and its infrastructure so much attention 💯