Provide release steps for Codeflare Instascale

[sutaakar]

Repository is missing a documentation providing instructions to release a new version. There is a brief mention of image release in https://github.com/project-codeflare/instascale#image-creation , however it is not clear if this is the only step needed to release a new version or if there are some other steps needed.

Readme file should be adjusted to describe steps taken to release a new Instascale version, possibly mentioning any external dependency.