Better usage examples in the quickstart

[confluence]

The quickstart guide in the docs should contain 1) examples of all the different session creation methods, and 2) some very basic examples of opening and interacting with images, changing properties, etc.. Currently the usage examples are very arbitrary, and picked by a non-astronomer (me) out of the available functionality. They should be replaced with more realistic examples of what a real user might want to do with the UI.

The quickstart is intended to be a very brief introduction to the software, so this should be a very small selection. This is separate from the more complete user guide which is also planned for the wrapper and the snippets UI.

This work should wait for the refactoring PR (#123) and the basic region support PR (#136) to be merged.