issue/630/add environment.yml

[lorenzonggl]

This PR addresses#630 . A new file, environment.yml, is created to allow users to work locally in a stable and fixed conda environment by running:

$ conda env create -f environment.yml
$ conda activate clmm

[coveralls]

coverage: 100.0%. remained the same
when pulling 31ba343 on issue/630/coda_environment
into e95f0e0 on main.

[marina-ricci]

@lorenzonggl : I think you need to add healpy. I got : ModuleNotFoundError: No module named 'healpy'

[marina-ricci]

Beware that you have to install clmm without the "--user"" then.

[m-aguena]

looks good!