created the read_csv and paths submodules

The goal of this branch was to solve issue #3 (closed) parent of #4 (closed) and #5 (closed).

We have developed the read_csv and the paths submodules that allow to the user to define the search and filtering criteria of their search through a csv file present in the /criteria folder of the project. This new method has been implemented in get_cmip6_data.ipynb.

During the development of this branch, we have unveiled several new issues linked to the current state of the notebook as described in #19 (closed).