* docs - running development branch instructions

* reorganized content into existing pages

* Jeff edits

Co-authored-by: Jeff Bruemmer <jeff@metabase.com>

* remove gh command, minor edits

* reorganizing step numbers

Co-authored-by: Jeff Bruemmer <jeff@metabase.com>

* Add whats new for driver authors in 0.42.0 [ci skip]

* Apply suggestions from code review [ci skip]

Co-authored-by: Jeff Bruemmer <jeff@metabase.com>

Co-authored-by: Jeff Bruemmer <jeff@metabase.com>

* raw tags

* index to start

* update toc link

* reference link

* Run percy (sanity check) visual tests in CircleCI

* Update path for visual tests

* Make `--folder` flag optional

* visual tests docs

Co-authored-by: Alexander Lesnenko <alxnddr@users.noreply.github.com>