Update Documentation with citation

[altairgomes]

This PR makes the following updates to documentation:

• Fixed links to the figures in Getting Started.
• Included the SORA paper in the citation.
• Updated the concat information with Slack.

I've also moved the Releases.rst to the documentation, separating each version into different files, improving organization.

Finally, i make some updates to the gitignore file.

[rcboufleur]

System requirements must be also updated. Especially cartopy version.