go run: cannot run non-main package

The entry point of each go program is main.main, i.e. a function called main in a package called main. You have to provide such a main package.

GAE is an exception though. They add a main package, containing the main function automatically to your project. Therefore, you are not allowed to write your own.

You need to use the main package, a common error starting with go is to type

package Main

instead of

package main