First Proposal : tutorial for optimizing docker images (#1747)

* Create .srour

* Delete .srour

* Create README.md

contributions/executable-tutorial/srour/README.md

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+# Assignment Proposal
+
+## Title
+
+Tutorial: Optimizing your Docker Images
+
+## Names and KTH ID
+  - Thomas Srour (srour@kth.se)
+## Deadline
+
+Task 2
+
+## Category
+
+Executable Tutorial
+
+## Description
+As Docker images can easily get very big very fast, for this task, I would like to make a Katacoda tutorial describing the many different ways of optimizing/ reducing the size of Docker images, for example minimizing the number of layers, caching and multistage builds.