Set up FOSSA scanner

[martijnthe]

We should set up a FOSSA scanner just like with the main jerryscript project.

• Set up FOSSA job for this repo
• Add badge to README.md

[martijnthe]

@akosthekiss Do you have control over the fossa.io account? Could you add this new repo to it?

[martijnthe]

Related issue: jerryscript-project/jerryscript#1759