some docs suggestions

[ismael-mendoza]

• change 'user guide' to 'workflow' -> workflow is a bit technical
• make create a new quick step guide tutorial like in other documentation (or make it clear this is a notebook, at least until you refactor it)
• remove DefaultSampling function definition in tutorial doc
• add version for galsim installation and a couple in the installation page (add version we tested it with)
• for developers installation -> put in docs