Writing a more descriptive README.md and other related files to get started

[salilmishra23]

I think having a descriptive README.md allows a new user to get most of the important details in one go.
We do provide this information in the docs(https://juliaimages.org/latest/install.html) but having it here would also be good.

I also propose a CONTRIBUTING.md file describing how can one start making a contribution to the package. It provides beginners a path to follow and makes their journey to their first contribution easier.

[johnnychen94]

• The docs(https://juliaimages.org/latest/install.html) is the documentation of the whole Julia Image ecosystem.
• This repository Images.jl, however, consists of many dependencies. It would be quite ambiguous to introduce too many details of other repos to Images.jl/README -- which part of it really belongs to this repo?

But yes efforts should be paid to make the documentation more descriptive:

• we can add some quick-to-start snippets in Images.jl/README.
• Perhaps adding some comparison (code simplicity, benchmark, etc.) to other languages will make this package more attractive. But I think this packages is not mature enough to do this right now.
• Also, I think there are few description to the relationship of this ecosystem at present.