Thanks for your reply.
When I type flutter channel master I get what appears to be a git pull from github.com/flutter/flutter and then these are the last lines in the output:
git: Please commit your changes or stash them before you switch branches.
git: Aborting
Switching channels failed with error code 1.
Is there some directory that we must be in that your article does not mention? I am new to Flutter so I don't know anything about its directory layout or any other aspects of Flutter, but I am very interested in something to build cross-platform desktop apps besides Electron.