Getting started docs - Migrating section: refactor some of the text for clarity and easy reading.Also removed some rogue tab characters in the source that I introduced in prior commits.
For consistency with the rest of the docs, removed manually line-wrapped HTML text.
No manual line breaks in HTML text as per custom.
Fixed to lowercase 'v' in 'v3.0'
Removed a trailing space at end of line.
Yet another  manually wrapped text line consolidated
fixed a </p> tag that was on its own line.
Merge pull request #10421 from StevenBlack/GSEdits6

Getting started docs - Migrating section: refactor the text for ...