Implement all the improvements from user testing and validation feedback

[antoniivanov]

After #2431 we will have list of improvements we want to make to the main README. This story aims to address some of those that are most critical.

[zverulacis]

• VDK about sentence needs to repeat itself in the repo once more
• Is getting started in the ingestion? Should it be somewhere else?
• The titles of each section should be as originally intended in Github - on the left
• The design of the buttons for each section can be improved
• If you need SUPPORT - join slack or open an issue
• first data job or hello world data job
• write - examples

[zverulacis]

PR open: #2654

I will have one more feedback session. Then I'll finalize the changes.

[zverulacis]

Todo:

There's no description of how to create a data job!

• There's no description of how to create a data job! - in the Getting Started guide !

[zverulacis]

Open to review. When the PR is merged, the ticket can be closed.