Fix instructions for building from source.
Fix instructions for building from source.

nukisman/elm-format-short,avh4/elm-format,nukisman/elm-format-short,nukisman/elm-format-short,nukisman/elm-format-short,fredcy/elm-format,avh4/elm-format,avh4/elm-format,nukisman/elm-format-short,fredcy/elm-format,avh4/elm-format,fredcy/elm-format