Template for PRs

[marimeireles]

We should standardize contributions.

[sleepypioneer]

Should include:

what, why and optional how questions as sections

[berlin-pyladies]

Information for how to set up a template https://docs.github.com/en/communities/using-templates-to-encourage-useful-issues-and-pull-requests/configuring-issue-templates-for-your-repository