Suggest adding to tsconfig after installing @types

[ajafff]

Ref: #28168 (comment)

@sandersn @DanielRosenwasser

[weswigham]

Small improvement: Have both messages. If a types field exists in the options, use this message, otherwise, use the old one. If a user doesn't have an explicit types option, then they shouldn't need to do anything - they'll be included automatically.

[ajafff]

@weswigham Sounds good to me. I'll open a follow-up PR.
Should there be a separate message if there is typeRoots in tsconfig?

[weswigham]

Hm; If either of the other messages sound confusing in that context, then I guess so.