fix: validation example

[lord007tn]

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

I changed the validation-example.js to pass the JSON validation schema.
and add a section in the readme.md file so people can have a quick access to make it work
Fixes #173

[Eomm]

Could you add a test for this new example?

We can make it consistent in this way

[lord007tn]

Still working on It
further in the project the Ajv validators seems to make fastify fail in some edge cases
I'm trying to find solutions and I will update it soon
with tests also

[lord007tn]

I added a working example that i've tried in my work project
and it works fine
still lacks unit testing
i would give it a try when i have more time
you could verify it

[fertolg]

If you go this route, then any additional schemas will need to be added to the validator instead of the normal fastify.addSchema usage, which may not be intuitive. See the note in the validator compiler docs.

Instead of defining an entirely custom validator, would passing the custom keyword as options when initializing fastify allow users to still rely on Fastify's private AJV implementation?

• See Fastify's AJV factory docs
• See the AJV keywords option

[lord007tn]

you made a good point
as myself I didn't use addSchema() but it's valid I will push changes

[mcollina]

lgtm