Add a rationale write up.

RATIONALE.md

@@ -0,0 +1,42 @@
+# Rationale for Mobile games with Corona SDK
+
+## Why games
+
+Almost everyone writing software in their mid twenties got started because they
+wanted to make video games. Games are engaging. The best games push on your
+imagination and critical thinking the same way a good book does. Games are a
+good place to get kids interested in programming because they're very visual,
+feedback is immediate, and they're software the kids can understand and build to
+their own desires. Moreover, kids can *share* games with other kids. There's
+nothing more motivating as a game designer (or software developer) than seeing
+someone use your work.
+
+With all that, games are hard. Games are the absolute hardest software to write
+for a lot of reasons. This class is going to be challenging for students and
+mentors, but it's also going to be really rewarding.
+
+## Why mobile?
+
+The computer of today's youth is the mobile device. Young kids and by extension
+prospective early coders are far more likely to have regular access to a mobile
+phone or tablet than a laptop computer. Furthermore, mobile devices are portable
+and encourage sharing by their ease of transfer and basic interface. Anyone who
+writes a game for a mobile device can hand that to their friend much more
+readily than they can share a computer program.
+
+## Why Corona
+
+We know we want mobile and we know we want games. From the above sections we see
+the challenges to amortize are cross-platform compatibility and ease of
+development. Of all available options for game development, Corona SDK is the
+most suitable for this course.
+
+* Corona uses a very simple programming language that is popular in the games world (Lua)
+* Corona supports Android and iOS devices
+* Corona is simpler than Unity, at the cost of some power
+* Corona projects are easier to distribute and extend
+
+There are reasons to do Unity-based programming both mobile and desktop in other
+classes but for now I think Corona offers more if we want to keep teh class
+accessible to younger students such as the ones we've been getting at Coder
+Dojo.

README.md

@@ -37,6 +37,8 @@ Section 5: Something Amazing!
 The target age range for this class is fifth grade through high school but
 younger coders who meet the requirements are welcome.
 
+##### See the [rationale](RATIONALE.md) for this course.
+
 [0]: section-00/
 [1]: section-01/
 [2]: section-02/