doc(*): switch from update-mathlib to leanproject (#2093)
* doc(*): switch from update-mathlib to leanproject
* Apply suggestions from code review
Co-Authored-By: sgouezel <sebastien.gouezel@univ-rennes1.fr>
* Use shiny new `leanproject new` and `leanproject get`
* documentation tweaks
* project.md tweaks
Co-authored-by: sgouezel <sebastien.gouezel@univ-rennes1.fr>
Co-authored-by: Patrick Massot <patrickmassot@free.fr>
Co-authored-by: Bryan Gin-ge Chen <bryangingechen@gmail.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
