additions to upright instructions and tidying up

This merge request updates the Upright microscope instructions

• Changes the note that other optics modules can be used on the first page, and conditionally adds this note to the basic optics module page, for Upright only.
• Uses the existing variables to add the third illumination platform nut to the stage preparation.
• Adds links to Gitlab and Forum in the help note on the main page.
• Tidies up wording in places