Refactor README to be easier to read through (#1731)

Preview: https://github.com/ADTC/svgo/blob/patch-1/README.md

* Split up code blocks by moving text outside them. (This also ensures
that the Copy function makes sense. _See screenshot:_)
* <img width="380" alt="image"
src="https://user-images.githubusercontent.com/6047296/211246090-64749e5f-3f1e-413b-be39-a99fa2f1b425.png">
* Remove the redundant list of default plugins and refer to the table
instead.
* Sort the table of plugins alphabetically. (It's easier to scan for a
plugin.)
  * _I suggest maintaining the sort when adding new items._
* Replace the enabled/disabled code in Default column with just Yes or
blank.
* Tabulate the "Other ways to use" section and remove redundant "as
a/an".
* Correct the word Donators to Donors.
* Add a new section called _Troubleshooting_.