SPARK-4040. Update documentation to exemplify use of local (n) value, fo...

This is a minor docs update which helps to clarify the way local[n] is used for streaming apps.

Author: jay@apache.org <jayunit100>

Closes #2964 from jayunit100/SPARK-4040 and squashes the following commits:

35b5a5e [jay@apache.org] SPARK-4040: Update documentation to exemplify use of local (n) value.

1 files changed, 8 insertions, 2 deletions

diff --git a/docs/configuration.md b/docs/configuration.md
index 685101ea5c..0f9eb81f6e 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -21,16 +21,22 @@ application. These properties can be set directly on a
 [SparkConf](api/scala/index.html#org.apache.spark.SparkConf) passed to your
 `SparkContext`. `SparkConf` allows you to configure some of the common properties
 (e.g. master URL and application name), as well as arbitrary key-value pairs through the
-`set()` method. For example, we could initialize an application as follows:
+`set()` method. For example, we could initialize an application with two threads as follows:
+
+Note that we run with local[2], meaning two threads - which represents "minimal" parallelism, 
+which can help detect bugs that only exist when we run in a distributed context. 
 
 {% highlight scala %}
 val conf = new SparkConf()
-             .setMaster("local")
+             .setMaster("local[2]")
              .setAppName("CountingSheep")
              .set("spark.executor.memory", "1g")
 val sc = new SparkContext(conf)
 {% endhighlight %}
 
+Note that we can have more than 1 thread in local mode, and in cases like spark streaming, we may actually
+require one to prevent any sort of starvation issues.  
+
 ## Dynamically Loading Spark Properties
 In some cases, you may want to avoid hard-coding certain configurations in a `SparkConf`. For
 instance, if you'd like to run the same application with different masters or different