Add troubleshooting section in README

README.md

@@ -15,7 +15,8 @@ Run [spark](https://spark.apache.org/) calculations from [Ammonite](http://ammon
    1. [Syncing dependencies](#syncing-dependencies)
 3. [Using with standalone cluster](#using-with-standalone-cluster)
 4. [Using with YARN cluster](#using-with-yarn-cluster)
-5. [Missing](#missing)
+5. [Troubleshooting](#troubleshooting)
+6. [Missing](#missing)
 
 
 
@@ -101,6 +102,24 @@ Ensure the configuration directory of the cluster is set in `HADOOP_CONF_DIR` or
 
 Before raising issues, ensure you are aware of all that needs to be set up to get a working spark-shell from a Spark distribution, and that all of them are passed in one way or another to the SparkSession created from Ammonite.
 
+## Troubleshooting
+
+### Getting `org.apache.spark.sql.AnalysisException` when calling `.toDS`
+
+Add `org.apache.spark.sql.catalyst.encoders.OuterScopes.addOuterScope(this)` on the same lines as those where you define case classes involved, like
+```scala
+@ import spark.implicits._
+import spark.implicits._
+
+@ org.apache.spark.sql.catalyst.encoders.OuterScopes.addOuterScope(this); case class Foo(id: String, value: Int)
+defined class Foo
+
+@  val ds = List(Foo("Alice", 42), Foo("Bob", 43)).toDS
+ds: Dataset[Foo] = [id: string, value: int]
+```
+
+(This should likely be added automatically in the future.)
+
 ## Missing
 
 Local clusters, Mesos, and Kubernetes, aren't supported yet.