Add openssf scorecard to readme.

Can't do the fancy badge, don't think shields.io has this owner.

README.md

@@ -57,6 +57,9 @@
 
 <br>
 
+[![OpenSSF Scorecard](https://api.securityscorecards.dev/projects/github.com/Ultimaker/Cura/badge)](https://api.securityscorecards.dev/projects/github.com/Ultimaker/Cura)
+
+<br>
 
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