Use conda to set GAMMAPY_DATA env variable

[HealthyPear]

This is just a minor documentation suggestion.

Since the installation requires the use of conda, you might as well instruct the user to set any environment variable using conda itself for the environment specific to the gammapy version in use, instead of using the shell which is global,

$ curl -O https://gammapy.org/download/install/gammapy-1.1-environment.yml
$ conda env create -f gammapy-1.1-environment.yml
$ conda activate gammapy-1.1
$ gammapy download notebooks
$ gammapy download datasets
$ conda env config vars set GAMMAPY_DATA=$PWD/gammapy-datasets/1.1
$ conda activate gammapy-1.1

[github-actions]

Merci! We will respond to your issue shortly. In the meantime, try import gammapy; gammapy.song()

[registerrier]

Thanks @HealthyPear . That's a very good suggestion.