Add introductory diagram

Author: sebromero

docs/01-threading-basics.md

@@ -3,7 +3,11 @@
 Threading Basics
 ================
 ## Introduction
-Threading is a concept that is used on many operating systems to run tasks in parallel. An Arduino example of two such tasks could be to read the position of a potentiometer knob while controlling a servo motor to follow that position. Running such tasks in parallel is also called multitasking. Previously Arduino sketches didn't support the concept of multitasking, unless you took specific measures to support it. With this so called single-threaded approach instructions in your Arduino sketch are executed one after another. If an instruction or a function call respectively makes the runtime environment wait for its execution to complete, it's called a "blocking" function. You may have encountered the limitations of this when interacting with multiple sensors and actuators at once. For example if you let a servo motor react to the data read from a distance sensor. While the servo motor is moving to its target position no further reading of the distance sensor can be done because the program waits until the servo is done moving. To solve this issue multitasking can be used which allows to "simultaneously" execute multiple task such as reading from a sensor and controlling a motor. In the context of multitasking a thread is basically a mechanism (provided usually by the operating system) to encapsulate a task to be run concurrently with others.
+Threading is a concept that is used on many operating systems to run tasks in parallel. An Arduino example of two such tasks could be to read the position of a potentiometer knob while controlling a servo motor to follow that position. Running such tasks in parallel is also called multitasking. 
+
+![Example of two tasks that ideally run in parallel.](assets/Arduino-Threads-Tasks-Example.svg)
+
+Previously Arduino sketches didn't support the concept of multitasking, unless you took specific measures to support it. With this so called single-threaded approach instructions in your Arduino sketch are executed one after another. If an instruction or a function call respectively makes the runtime environment wait for its execution to complete, it's called a "blocking" function. You may have encountered the limitations of this when interacting with multiple sensors and actuators at once. For example if you let a servo motor react to the data read from a distance sensor. While the servo motor is moving to its target position no further reading of the distance sensor can be done because the program waits until the servo is done moving. To solve this issue multitasking can be used which allows to "simultaneously" execute multiple task such as reading from a sensor and controlling a motor. In the context of multitasking a thread is basically a mechanism (provided usually by the operating system) to encapsulate a task to be run concurrently with others.
 
 In the historic single-threaded execution of Arduino sketches the complete program logic is contained within the `*.ino` file. It contains both a `setup()` function, which is executed only once at program start, and a `loop()` function, which is executed indefinitely. A single-threaded Arduino project can theoretically contain multiple `*.ino` files but you can define `setup()` or `loop()` only once.
 In order to support multi-threaded (or parallel) sketch execution a new file type called the `*.inot` file is introduced.