[Docs enhacement] TypescriptAddMissingImports don't work in javascript files without checkJs

[serranomorante]

TypescriptAddMissingImports seems to not work for javascript projects that don't specify the checkJs: true option in it's jsconfig.json.

This was mentioned in the deprecated version of this plugin:

Note: :TSLspImportAll depends on tsserver diagnostics, meaning that the function won't work for JavaScript files unless you set "checkJs": true inside tsconfig.json / jsconfig.json.

If that's still the case we should mention it here too.

[jose-elias-alvarez]

Do any commands work in JavaScript projects without the option enabled? This is more of a typescript-language-server config issue than something specific to this plugin (the situation with nvim-lsp-ts-utils wasn't exactly the same, since we relied on parsing generated diagnostics).