Improve README

I came across `chisel` today. It looks like an exciting tool, but unfortunately the README doesn't make it very clear what its purpose is.

Could you please expand the README? Some suggestions:

* Start with an overview of what the tool is
* Give some examples of usage with explanations of what the commands do
* Define any new terms you've invented (e.g. I see mention of `slice` but it's not very clear what that term means here)
* Compare to similar projects in the space, noting when you might use the other project or when you might use `chisel`

Start by reading the existing README and exploring chisel's usage so the overview, examples, terminology, and comparison are accurate. Done means the README explains the tool's purpose, demonstrates commands with explanations, defines terms such as “slice,” and describes when similar projects may be preferable.

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