Notes for "getting started" guide

[avh4]

In answer to a question on Elm slack re getting started with elm-format, I thought this answer might be good to have in the official documentation:

it’s recommended to enable “format on save” for whatever editors (the guideline for plugin authors is that hopefully it enables that by default)

To initially format (or for folks who don’t want to format on save), elm-format . on the command line is recommended.

And to enforce formatting on CI, elm-format --validate . is recommended.