add mesmer_m example script (MESMER-group#491)

* add mesmer_m example script

* changelog

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

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* remove unused imports

* adjustments

* replace script with notebook

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

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* restructure and add some headings

* remove inputs

* add some comments

* typos

* date_range: update freq string (MESMER-group#504)

* date_range: update freq string

* add freq conditionals

* reference: only year as link (MESMER-group#505)

* nits

* more info on time coordinate

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* update comment & clear output

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Mathias Hauser <mathias.hauser@env.ethz.ch>
Co-authored-by: Mathias Hauser <mathause@users.noreply.github.com>

CHANGELOG.rst

@@ -63,6 +63,7 @@ that this led to some numerical changes compared to the MESMER-M publication
   `#421 <https://github.com/MESMER-group/mesmer/pull/421>`_).
 - move the harmonic model and power transformer functionalities to the stats module (
   `#484 <https://github.com/MESMER-group/mesmer/pull/484>`_).
+- add example script for MESMER-M workflow (`#491 <https://github.com/MESMER-group/mesmer/pull/491>`_)
 
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