chore(docs): grammatical tweaks to migration guide (gatsbyjs#14505)

* Made the doc easier to read

- Moved a lot of sentences into active voice
- Removed unnecessary words and sentences
- Fixed some grammatical errors
- Removed potentially confusing emojis as a literary device
- Split up some long sentences into shorter ones
- Added a link to https://www.gatsbyjs.org/blog/2018-06-08-life-after-layouts/ in the layouts section to help people move from Gatsby's layout behavior in v1
- Capitalized instances of "Babel" that were lowercase

* Adding a misssing "the"

Co-Authored-By: Mike Allanson <[email protected]>

* Simplify sentence

Co-Authored-By: Mike Allanson <[email protected]>

* Explain Gatsby's behavior in v1 vs v2 for node data

Co-Authored-By: Mike Allanson <[email protected]>

* chore: format