We want all developers to be successful and adding instructions is the best way to do this. Users might be new, or just working under pressure - so let's try not to make them think!
Should the user clone the repo? Install a library into their own project? Something else? Spell out what the user should do here.
Are there dependencies? How should those be installed? Bear in mind that not all developers will be familar with the tech stack or dependency manager (someone new to programming, or just loving your project despite having expertise in different technologies) so go for more detail, not less.
What else is needed? Nexmo key/secret/signature secret/something else? Do they need to create an application, buy a number, register a JWT? Link to documentation segments as you need to, and include instructions on which files the configuration should go into.
Pro-tip: experienced developers are experienced skip-readers. Include every step and you include less experienced developers; our senior devs will find their way perfectly well too.