added example implementing custom store using Sequelize ORM for PostgreSQL database; renamed example-custom to example-knex; added links of examples implementing custom-store to README.md

[the-vishal-kumar]

…reSQL database

renamed example-custom to example-knex
added links of examples implementing custom-store to README.md

Checklist

• run npm run test
• 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

[jsumners]

👎

Docs should not link out to a third party repository.

[the-vishal-kumar]

Docs should not link out to a third party repository.

I've updated the links in README.md to Fastify-Rate-Limit Repository

[Eomm]

I think this example is really useful and I would like to suggest a little refactoring to apply the best practice we sponsor thought the plugin system!

[Eomm]

I think that moving this class to a file would let the user understand better how to organize the source.

Moreover, this would avoid having a global sequelize object and it would be really more useful to users to adapt to their fastify instance

(I saw there is the same issue in the knex example and I think it should be improved as well - not an issue with this PR)

[jsumners]

LGTM

[mcollina]

Lgtm