[NEW] Explain changes field in PR template

Pull request checklist

Please check if your PR fulfills the following requirements:

[x] You can build successfully the whole project with your changes locally
[x] You use the coding conventions and the naming conventions of the project
[x] You use tabs for indentation
[x] You make sure that your PR is not a duplicate
[x] This PR is ready to be reviewed and merged
[x] This PR merges into the development branch or in the specific branch of the feature you want to merge into
[x] There is no TODO in the code
[x] There is no spelling or grammatical errors in the code
[x] Details of the issue or feature are documented below
[x] This PR is not a breaking change (e.g. changes that would cause existing functionality to change)

Français `fr`
Explain changes field in PR template

Before merging this PR, you will need the approval of at least one of the following people:

So be patient ;)