docs: how to switch between and configure IDEs

[ghuntley]

Opening in response to customer feedback that the Gitpod documentation does not have a section or page which goes into detail how switch between editors.

See also:

• https://www.gitpod.io/docs/feature-preview/
• https://community.gitpod.io/t/green-run-button-disappeared-on-my-python-repository/2987/6?u=ghuntley

[akosyakov]

It is covered here already: https://www.gitpod.io/docs/feature-preview/#default-ide and this link was mentioned to a user before his question.