Add watch task

- Also, turn digests off in development

Procfile.dev

@@ -0,0 +1,2 @@
+web: bin/rails server -p 3000
+css: bin/rails dartsass:watch

bin/dev

@@ -0,0 +1,8 @@
+#!/usr/bin/env sh
+
+if ! gem list foreman -i --silent; then
+  echo "Installing foreman..."
+  gem install foreman
+fi
+
+exec foreman start -f Procfile.dev "$@"

config/environments/development.rb

@@ -51,6 +51,9 @@
   # Suppress logger output for asset requests.
   config.assets.quiet = true
 
+  # To see the latest stylesheet changes, if running Sass in watch mode.
+  config.assets.digest = false
+
   # Raises error for missing translations.
   config.i18n.raise_on_missing_translations = true