Add brief tutorial to README.md

Author: Mark Hatton

README.md

@@ -1,4 +1,61 @@
-AWS DataPipeline DSL for Scala
-==============================
+# AWS DataPipeline DSL for Scala
 
-More here soon...
+A Scala domain-specific language and toolkit to help you build and maintain AWS DataPipeline definitions. 
+
+This tool aims to ease the burden of maintaining a large suite of AWS DataPipelines.  At Shazam, we use this tool to
+define our data pipelines in Scala code and avoid the boilerplate and maintenance headache of managing 10s or 100s of
+JSON pipeline configuration files. 
+
+Benefits:-
+- Write and maintain Scala code instead of JSON configuration
+- Use the DSL's `>>` syntax to clearly express dependencies between your pipeline's activities
+- Share code/configuration between your pipeline definitions
+- Never write `dependsOn` or `precondition` again, this library manages all ids and object references for you
+- Add your own wrapper around this library to predefine most your most commonly-used data pipeline objects
+
+## Tutorial
+
+Build the compiler using `sbt`:
+```
+$ sbt assembly
+```
+
+Create a "Hello World" AWS Data Pipeline definition Scala file:
+```
+object HelloWorldPipeline {
+
+  import datapipeline.dsl._
+
+  val pipeline =
+    AwsDataPipeline(name = "HelloWorldPipeline")
+      .withSchedule(
+        frequency = Daily,
+        startDateTimeIso = "2018-01-01T00:00:00"
+      )
+      .withActivities(
+        ShellCommandActivity(
+          name = "Echo Hello World",
+          workerGroup = "my-task-runner",
+          Command("echo 'Hello AWS Data Pipeline World!'")
+        )
+      )
+
+}
+```
+
+Use the compiler to produce JSON from our Scala definition:
+
+```
+$ java -jar target/scala-2.12/datapipeline-compiler.jar HelloWorldPipeline HelloWorldPipeline.scala
+Writing pipeline definition to: ./HelloWorldPipeline.json
+``` 
+
+The output JSON file contains your pipeline definition ready to deploy to AWS.
+
+## Supported AWS DataPipeline Objects
+
+For details see [Supported Objects](Supported%20Objects.md).
+
+## License
+
+This tool is licensed under [APL 2.0].

src/main/scala/datapipeline/compiler/AwsDataPipelineCompiler.scala

@@ -62,12 +62,14 @@ object AwsDataPipelineCompilerHelpers {
 
     if (!clazz.getDeclaredFields.map(_.getName).contains(PipelineField)) fail(
       s"""Error: The class $className does not have a field named '$PipelineField'.
-         |Your pipeline definition singleton should include a field named 'pipeline' of type datapipeline.dsl.PipelineBuilder,
+         |Your pipeline definition singleton should include a field named '$PipelineField' of type datapipeline.dsl.PipelineBuilder,
          |e.g.:
          |
-         |object DataPipeline {
+         |object MyDataPipeline {
          |
-         |  val pipeline = datapipeline.dsl.AwsDataPipeline(name = "my-pipeline", ...)
+         |  import datapipeline.dsl._
+         |
+         |  val $PipelineField = AwsDataPipeline(name = "MyDataPipeline", ...)
          |
          |}
         """.stripMargin