added first, introduction episode content.

Author: Toby Hodges

_episodes/01-introduction.md

@@ -3,13 +3,30 @@ title: "Introduction"
 teaching: 0
 exercises: 0
 questions:
-- "Key question"
+- "What is Common Workflow Language?"
+- "Why might I want to learn to use CWL?"
 objectives:
-- "First objective."
+- "Learn what CWL is."
+- "Learn about the motivation behind the project."
 keypoints:
-- "First key point."
+- "CWL describes command line tools and workflows."
+- "CWL is not software."
+- "Descriptions in CWL aid portability between environments"
 ---
-Content here
 
-{% include links.md %}
+CWL is a way to describe command line tools and connect them together to create
+workflows.  Because CWL is a specification and not a specific piece of
+software, tools and workflows described using CWL are portable across a variety
+of platforms that support the CWL standard.
+
+CWL has roots in "make" and many similar tools that determine order of
+execution based on dependencies between tasks.  However unlike "make", CWL
+tasks are isolated and you must be explicit about your inputs and outputs.  The
+benefit of explicitness and isolation are flexibility, portability, and
+scalability: tools and workflows described with CWL can transparently leverage
+technologies such as Docker, be used with CWL implementations from different
+vendors, and is well suited for describing large-scale workflows in cluster,
+cloud and high performance computing environments where tasks are scheduled in
+parallel across many nodes.
 
+{% include links.md %}