Add default readme for generated project

[khattakdev]

Closes #362

This PR took me a whole day to debug. There is something wrong with tests, maybe with a specific npm package.
When adding a README.md template in app and app-ts like following

# Getting Started with Fastify-CLI

This project was bootstrapped with [Fastify-CLI](https://github.com/fastify/fastify-cli).

This results in the failure of test suitss. A workaround for this is to add content like the following:

# Getting Started with Fastify-CLI

###### This project was bootstrapped with [Fastify-CLI](https://github.com/fastify/fastify-cli).

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

[mcollina]

The changes looks good but the tests should be fixed

[khattakdev]

The changes looks good but the tests should be fixed

This is quite strange. While making this PR, I tested it and it was working fine. Now I realized, it works on fine on windows machine but fails on Unix (tried on WSL2)
Windows:

WSL2:

I've been working on this since yesterday but couldn't find out what's the exact issue. Any help would be really appreciated.

[khattakdev]

With the new commit, this should work fine now. It was failing in package.json (description file). I didn't know it auto copy the first paragraph from README and add it to description

[mcollina]

lgtm