Update build.mill

Author: lihaoyi

example/scalalib/basic/1-simple/build.mill

@@ -27,7 +27,9 @@ object `package` extends RootModule with ScalaModule {
 // You can download this example project using the *download* link above
 // if you want to try out the commands below yourself. The only requirement is
 // that you have some version of the JVM installed; the `./mill` script takes
-// care of any further dependencies that need to be downloaded.
+// care of any further dependencies that need to be downloaded. All examples
+// in this documentation site are executable and are continually exercised as 
+// part of Mill's CI workflows.
 //
 // The source code for this module lives in the `src/` folder.
 // Output for this module (compiled files, resolved dependency lists, ...)