2nd sentence - Explaining the tool to folks in the general web domain what it can do for them.
3rd sentence - Explaining where to learn how to use the tool if you've stumbled across it but web is not your area of expertise.
All that info fits in nearly 25 words then it lists the options for the tool and jumps straight into multiple examples (with outputs!). If the only explanation had been "htmlq: like jq, but for HTML" I'd agree but having the comparison to explain what it does isn't a bad thing it's _only_ having the comparison that would be bad.
Personally I think this is a model example of a opening for a Github readme.