Fix #599: Expand a bit the sbt setup on the doc/project/ page.

Author: sjrd

doc/project/index.md

@@ -4,7 +4,7 @@ title: Scala.js project structure
 ---
 
 
-Scala.js comes with an sbt plugin that facilitates compiling, running and testing with Scala.js. For a quick start, 
+Scala.js comes with an sbt plugin that facilitates compiling, running and testing with Scala.js. For a quick start,
 have a look at our [basic tutorial](../tutorial/basic/).
 
 Load the sbt plugin (`project/plugins.sbt`)
@@ -16,8 +16,13 @@ addSbtPlugin("org.scala-js" % "sbt-scalajs" % "{{ site.versions.scalaJS }}")
 Enable the plugin on the sbt project (`build.sbt`):
 
 {% highlight scala %}
-lazy val root = project.
-  enablePlugins(ScalaJSPlugin)
+lazy val root = project
+  .in(file("."))
+  .enablePlugins(ScalaJSPlugin)
+  .settings(
+    // for an application with a main method
+    scalaJSUseMainModuleInitializer := true,
+  )
 {% endhighlight %}
 
 If you are using a `Build.scala` definition, import the following: