Update documentation for ReSharper 2020.2

[jozefizso]

Hi, could you update ReSharper SDK documentation for 2020.2 release to have up-to-date guide for writing extensions for ReSharper 2020?

[matkoch]

The documentation has been updated continuously ever since (see https://www.jetbrains.com/help/resharper/sdk/recently_updated.html). ReSharper and Rider are extensible in many ways, which makes it unfeasible to document every bit. Again, if you explain what you're looking for, I probably can help.

[jozefizso]

There are tens of articles which are not even written yet about writing PSIs...

[matkoch]

Are you intending to write PSI support for another language?