developer-roadmap Add new roadmap for mobile developers (Mobile Roadmap)

What roadmap is this issue about?

[ ] Frontend Roadmap
[ ] Backend Roadmap
[ ] DevOps Roadmap
[ ] All Roadmaps
[x] Missing Roadmap (Mobile)

What is this issue about?

[ ] Discussion for a pull request I would want to open.
[x] Addition of a new item
[ ] Removal of some existing item
[ ] Changing in arrangement
[x] General suggestion
[ ] Sharing an Idea
[ ] Something else

Please acknowledge the below listed

[x] This is not a duplicate issue. I have searched and there is no existing issue for this.
[x] I understand that these roadmaps are highly opinionated. The purpose is to not to include everything out there in these roadmaps but to have everything that is most relevant today comparing to the other options listed.
[x] I have read the contribution docs before opening this issue.

Enter the details about the issue here

When i just saw that there was a section for Web Dev Roadmap, that would be nice if we had a roadmap for mobile developers! The roadmap could guide between the basics of mobile what to learn first, native development (iOS or Android) and cross-platform development with some frameworks suggestions as React Native, Flutter or Ionic for example.