Merge branch 'threshold' into 'master'

Add binarization

See merge request !2

modules/binarization.md

+# Image binarization 
+
+## Requirements
+
+To understand this episode you need to know:
+
+- A
+- B
+- C
+
+## Motivation
+
+Few sentences.
+
+## Learning objectives
+
+- Understand the relationship between an intensity image and a derived binary image.
+- Execute binarization on an image.
+
+## Concept map
+
+- Intensity image --- threshold ---> Binary image
+- 
+
+## Example
+
+
+## Activity
+
+
+## Formative assessment
+
+Quizz or something
+
+## Follow-up material
+
+- [http:// ](next module in this repo)
+
+## Learn more
+
+External links...
+