Modified the PR template to include README.md update reqirement if ne…

[bgorski]

…cessary

Description (*)

With the introduction of the README.md template, there is a requirement of describing module installation, structure and extension points in the readme.
We need to pay special attention to README.md always being up to date, because an outdated readme can do more harm than good. This is why all code contributors need to be aware that they are supposed to modify README.md as well when they create modifications that affect any of readme predefined sections.

Related Pull Requests

Fixed Issues (if relevant)

1. Fixes magento/storefront-message-broker#<issue_number>

Questions or comments

Code Review Checklist (*)

See detailed checklist

• Story AC is completed
• proposed changes correspond to Magento Technical Vision
• new or changed code is covered with web-api/integration tests (if applicable)
  • expected results in test verified with data from fixture
• no backward incompatible changes
• Class usage: magento/storefront-message-broker repo don't use directly classes from magento/saas-export repo and vise-verse
  • Check composer.json dependencies
• Legacy code is deleted