How to install and make it run

I have download the zip file and unzip it in my path ~/i3-focus-last

after save the following setting in my i3 config file

```
bindsym $mod+b exec ~/i3-focus-last/main.go switch
exec --no-startup-id "~/i3-focus-last/main.go"
```

and reboot. but then I press the mod and b together and nothing change.