[Feature] Add translation documentation for people wanting to help translating

[Dynnammo]

Context

As a user, I would like to help translating Claper

Frustration

~No documentation whatsoever about it in the README~ Current documentation is about developing, we should complete it with translation documentation.

Solution

Provide a CONTRIBUTING.md file with all contribution possibilities (development, translation, sponsoring, etc.)

[alxlion]

Yes, we had to stop using poeditor.com because it's too limited and the integration with the project is not so smooth. So I'll document the translation process using the PO files soon.

[Dynnammo]

Yes, we had to stop using poeditor.com because it's too limited and the integration with the project is not so smooth. So I'll document the translation process using the PO files soon.

I think Crowdin or Weblate are battle-tested solutions (which I use for other projects). If help needed I may help.

[eduproinf]

I would like to help with translation, so looking foward to hearing from this HOWTO about the translation process

[alxlion]

The translation process is now explained in the CONTRIBUTING.md on the dev branch.