On the commandline navigate into the directory ./frontend and run go generate, that will create main.wasm file in ./static.
2. Static files
Make a copy of the wasm_exec.js file from $GOROOT/misc/wasm/ directory and put it in the ./static directory. This must be from the same golang version that you used to build main.wasm.
3. Running
After steps 1 and 2, on the commandline navigate into the directory containing main.go and run go run main.go. Then in your favorite web browser navigate to localhost:8081.