message: Add changelog update
diff: * Added support for tracking opening, closing and changing of virtual documents that don't exist on disk. (PR: [#2436](https://github.com/OmniSharp/omnisharp-vscode/pull/2436)) _(Contributed by [@NTaylorMullen](https://github.com/NTaylorMullen))_
  +* Enabled IDE features for .cs files that are not part of a project. (PR: [#2471](https://github.com/OmniSharp/omnisharp-vscode/pull/2471), [omnisharp-roslyn#1252](https://github.com/OmniSharp/omnisharp-roslyn/pull/1252))
  +
  #### Misc
  * Added a prompt to "Restart OmniSharp" when there is a change in omnisharp "path", "useGlobalMono" or "waitForDebugger" settings.(PR: [#2316](https://github.com/OmniSharp/omnisharp-vscode/pull/2316))
  