Add the 'Conditionals' lesson to csintro. (#428)

docs/courses/csintro/conditionals/overview.md

@@ -0,0 +1,30 @@
+# Introduction
+Computer programs are instructions telling the computer how to process input and deliver output. 
+An important part of programming is telling the computer WHEN to perform a certain task. 
+For this, we use something called ‘conditionals’.  Conditionals get their name because a certain Condition or Rule has to be met.
+
+Students are all already familiar with the concept of conditionals in their daily lives!
+
+Have they ever had their parents say..?
+* “If you clean your room, you can go out with your friends.”
+* “If your homework is done, you can play video games.”
+* “If you do your chores all week, you get your allowance, else you are grounded.”
+
+These are all conditionals! Conditionals follow the format of IF this, THEN that.
+>**IF** (condition is met), **THEN** (action performed)
+
+Have the students share a few conditionals from their own lives with the class or within small groups.
+
+Note: For older students, you can have them add the ELSE portion of a conditional.
+>**IF** (condition is met), **THEN** (action performed), **ELSE** (different action performed)
+
+Example:
+* IF it is snowing, THEN wear boots, ELSE wear shoes.
+
+The ELSE portion makes sure that a different action is performed in either case. Without the ELSE action, your students might be barefoot! 
+
+![If-Then workflow](/static/courses/csintro/conditionals/if-then-workflow.png)
+
+Tell the students that they will be acting out some conditionals as though the whole class is a computer program for a game. Each student will perform a described action if the indicated condition is met. 
+
+**Note:** This activity can be done as a whole class or in smaller groups or as a pencil and paper activity.