Improvements in element-array-ephys tutorial and README

[MilagrosMarin]

Only updates related to markdowns and those agreed upon for the element-deeplabcut tutorial will be integrated in this PR:
- [x] Insert pipeline architecture and flowchart at the beginning of the tutorial
- [x] Highlight the main steps in the index
- [x] Add tutorial setup
- [x] Simplified DataJoint pipeline design for this element
- [x] Organize step-by-step procedures
- [x] Add results visualization section
- [x] Add a concise summary
- [x] Move documentation and tutorials as a section to the end

[kushalbakshi]

Looks good @MilagrosMarin. Thank you for updating the tutorial. There are a few minor changes that I will update in a follow up PR since it's a little difficult to make suggestions to Jupyter notebooks on GitHub.