Add 'Arrays' lesson to csintro. (#436)

docs/courses/csintro/arrays.md

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+# Arrays
+
+This lesson covers storing and retrieving data in an ordered fashion using Arrays.  Introduces JavaScript as an alternate way of creating and modifying code. Uses a melody as a list/array of notes.
+ 
+## Lesson objectives
+Students will...
+* Explain the steps they would take to sort a series of numbers
+* Recognize three common sorting algorithms
+* Learn
+* Apply
+ 
+## Lesson structure
+* Introduction: Arrays
+* Unplugged Activity: Different Sorts of People
+* Micro:bit Activity: Headband Charades, Starry Starry Night
+* Project: Make a Musical Instrument
+* Assessment: Rubric 
+* Standards: Listed
+ 
+## Lesson plan
+
+1. [**Overview**: Arrays](/courses/csintro/arrays/overview)
+2. [**Unplugged**: Different sorts of people](/courses/csintro/arrays/unplugged)
+3. [**Activity**: Headband charades](/courses/csintro/arrays/activity)
+4. [**Project**: Musical instrument ](/courses/csintro/arrays/project)
+
+## Related standards
+
+[Targeted CSTA standards](/courses/csintro/arrays/standards)