How do you run stash in GitHub Desktop on Windows?
The feature is available in Sourcetree but I'm unable to find it in GitHub Desktop.
GitHub Desktop for Windows doesn't support stash. The only stash-like feature it has is that it will allow you to switch branches if you have uncommited changes. Source
Update: GitHub Desktop V2.0.0 now supports stash (Issue 6107). Now when switching branches, you'll be prompted to either leave your changes on the current branch (stash) or bring your changes over to the other branch.