docs: set defaultFormatter to correct value in README

[jareddellitt]

Formatting wasn't working and after checking the settings, the current value in the README causes a "Value not accepted" warning. The auto-suggest shows remote-com-oss.dexter-lsp which seems to work.

[JesseHerrick]

Thanks for the contribution @jareddellitt! The problem here is that our Cursor extension has a different namespace than the VS Code one due to the OpenVSX namespace for remoteoss being taken. So the real answer is that it depends on which editor you're using, but Cursor and VS Code are so similar that it feels odd having a separate config section for each.

Could you instead change this to have both lines and reference which editor each one goes to? So the line you're adding is for Cursor and the other line is for VS Code.

[jareddellitt]

@JesseHerrick my bad! Updated.