Manual Code Changes URL doesn't work anymore

I added apollo using `vue add apollo` and I got this warning:
```
WARN  apollo  Your main file couldn't be modified. You will have to edit the code yourself:
https://github.com/Akryum/vue-cli-plugin-apollo#manual-code-changes
```
but the URL doesn't work anymore. I guess, that it was moved. It's not that big of a deal but I thought I'll add an issue in case that no one noticed before :)