the "validation" assignment lacks details for getting/using Joi

The assignments so far have included instructions on installing additional modules for things not built into Node.js, it would be a good idea to mention how to install Joi, and the require call for it.

I'm not sure what the phrase "Joi information can also be found in `node_modules`" is supposed to mean, but as a learner I'm not going to dig through the node_modules directory structure in the hopes of finding a manual. A link to https://www.npmjs.com/package/joi would be far more valuable. However, that's the generic documentation, and is actually a mean thing to throw at a new learner, so linking to the specific thing that is relevant to this exercise will be important.

On a related note, "The solution will just check that a Validation object exists within the configuration for breed, not any specific validation." makes the hint overly detailed for the assignment. It would be more conducive to learning if the assignment then went on to say "so for now simply use the following code as value for the `validate` property, we'll be building on this in the next exercise". If this assignment does not test actually using Joi, it should not come with hints that imply someone needs to learn how to use Joi right now.