Updated GRASS GIS Docker Image Documentation

[bsurajpatra]

This update refines the GRASS GIS Docker image documentation by improving structure, ensuring accuracy in commands, and updating links to the latest versions. It simplifies the instructions for users to easily pull and use the appropriate Docker images for different environments like Alpine, Debian, and Ubuntu.

Solves #470

[veroandreo]

Thanks for your contribution, @bsurajpatra. Issue #470 however was really about documenting the usage of grass dockers and not copying the same information that was already there in a simpler way, along with removing the donate dialog.

In any case, the whole issue of docker doc and what info goes where seems to be on stand-by (see OSGeo/grass#4421, OSGeo/grass#4428, #427).