Doc - First step points to ruslo/hunter/wiki which does not exist

[Doc - First step](https://hunter.readthedocs.io/en/latest/quick-start/boost-components.html) has link to [HUNTER_ROOT](https://github.com/ruslo/hunter/wiki/usr.variables#hunter_root). This link is broken. I'm not sure where hunter wiki is hosted now.

```
First step
Set [HUNTER_ROOT](https://github.com/ruslo/hunter/wiki/usr.variables#hunter_root) environment variable to
```