remove old artefacts + face-lift in 01_start.R, a_start.Rmd and fill_desc() [FR]

[ilyaZar]

remove old artefacts of set_golem_options() from docs + improve docs

Sorry I was working (too slowly !) on the now closed #1040 :)

• there is some un-updated stuff in 01_start.R and a_start.Rmd regarding set_golem_options
• add some more documentation

I’ll leave the suggestions here, maybe it will become useful at some point

but feel free to close at any point ! !

[ColinFay]

closed via #1047