Switch doc to point to Spectrum

I noticed in the Gitter chat that you have moved discussion here. However, the docs are still pointing to Gitter
https://www.theia-ide.org/doc/index.html under Feedback.

[original thread by Tyler Hodgkins]

Thank you for pointing it out @tyler-hodgkins :slight_smile:
You can open an issue on the docs and website repo here https://github.com/theia-ide/theia-website

We already have an issue about this: https://github.com/theia-ide/theia-website/issues/32