PR task in 0. Git Basics subtopic

[usides]

This issue is a response to Ivan Tytarenko's request.

Subtopic 0. Git Basics has a task (PR to Kottans/mock-repo) that for new GitHub users hard to complete without watching a tutorial from subtopic 2. GitHub and Collaboration.
0. Git Basics has information about using Git in the local environment, but the task implicates that a student knows about forking and PRs.

As a solution, I can propose to combine subtopics 0. Git Bash and 2. GitHub and Collaboration with all tasks that they have.