README.md: correct "AWS Firecracker" references (#186)
README.md: correct "AWS Firecracker" references (#186)

* README.md: correct "AWS Firecracker" references

... to be just "Firecracker" (AWS is not part of the name). Also point to the upstream open source project homepage, rather than an AWS blog.

cf-unik/unik,cf-unik/unik,cf-unik/unik,cf-unik/unik,cf-unik/unik,cf-unik/unik,cf-unik/unik