(docs): improve test watch mode docs

[agilgur5]

• it was not clearly stated that CI=true was what needed to be added,
  so explicitly state that

• similarly, --color was an unnecessary option to pass and may have
  caused confusion, potentially making users believe that it was
  necessary in order to disable watch mode

  • also, --color does not seem to be a valid option of Jest, but
    --colors (note the s) is used to force highlighting in non-TTY

• also, properly format package.json example as JSON, including the
  "scripts" section

• and add a test:watch script for context, making more explicit the
  difference between non-watch and watch mode

Follow-up to #385 , related to #319, #366 . Though this documentation does make me wonder whether it makes sense to have --watch as a default. It's much more intuitive to pass --watch than to prefix with CI=true

[swyxio]

feel free to propose --watch in a separate issue. altho i think if u followed those issues, jared had a strong opinion that watch should be default

[agilgur5]

altho i think if u followed those issues, jared had a strong opinion that watch should be default

Unless I'm missing something, I think this is the only comment Jared made on it: #319 (comment) , which didn't seem strong?

But yea would be a separate issue, perhaps that should be voted on by users

[swyxio]

its not really up to a vote, this is Jared's project. but do what you think is right :)

[swyxio]

heads up - we have decided to undo this move. will not run in watch mode by default. sorry for the flipflop. #408