Add 'Coordinates' lesson to csintro. (#432)

docs/courses/csintro/coordinates.md

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+# Coordinate grid and LEDs
+
+This lesson introduces the use of coordinates to store data or the results of mathematical operations. It gives students practice programming for the LEDs of the micro:bit screen using coordinates. And introduces the basic game blocks of MakeCode.
+
+## Lesson objectives
+
+Students will...
+* Understand that the 5 x 5 grid of LEDs on the micro:bit represent a coordinate grid with the origin (0,0) in the top left corner.
+* Understand that the values of the x coordinates range from 0 through four and increase from left to right.
+* Understand that the values of the y coordinates range from 0 through four and increase from top to bottom.
+* Learn how to refer to an individual LED by its x & y coordinates.
+* Learn how to plot (turn on) and unplot (turn off) individual LEDs and how to toggle between these two states.
+* Learn how to check the current on or off status of an individual LED as well as check and set the brightness level.
+* Apply the above knowledge and skills to create a unique program that uses coordinates as an integral part of the program.
+
+## Lesson structure
+
+* Introduction: Coordinate Grid
+* Unplugged Activity: Battleship
+* Micro:bit Activities: Animation and Patterns
+* Project: Screensaver or Game
+* Assessment: Rubric 
+* Standards: Listed
+
+## Lesson plan
+
+1. [**Overview**: Coordinate grid and LEDs](/courses/csintro/coordinates/overview)
+2. [**Unplugged**: Battleship](/courses/csintro/coordinates/unplugged)
+3. [**Activity**: Animation and patterns](/courses/csintro/coordinates/activity)
+4. [**Project**: Screensaver or game](/courses/csintro/coordinates/project)
+
+## Related standards
+
+[Targeted CSTA standards](/courses/csintro/coordinates/standards)