Update the structure of "Features" section in README
This is the first iteration of making the README more clear.
This MR does the following changes:
- It introduces subheadings and moves the bullet points into their respective categories
- Removes bullet point formatting in favour of normal text for the new "Sidebar" and "Status bar" headings
- Mentions the exact command name for each command mentioned as a feature
Few other changes are explained directly on the diff.