add cii badge to readme.md

signed-off-by: Nanci Lancaster <[email protected]>

Author: Nanci Lancaster

README.md

@@ -43,3 +43,5 @@ Please join us during our online community meetings. Details can be found on our
 You can chat with us on Kubernetes Slack in the #carvel channel and follow us on Twitter at @carvel_dev.
 
 Check out which organizations are using and contributing to Carvel: [Adopter's list](https://github.com/carvel-dev/carvel/blob/master/ADOPTERS.md)
+---
+[![OpenSSF Best Practices](https://bestpractices.coreinfrastructure.org/projects/7746/badge)](https://bestpractices.coreinfrastructure.org/projects/7746)