Add an example of how to add your client IP to the container hosts file

Signed-off-by: Sven Dowideit <SvenDowideit@home.org.au>

inspired by #8395 - thankyou to @lwoodson 
@brasic contributed a mac version of the hostip command for our team.  You might want to call out that this is platform specific and offer the alternative.

```
alias hostip="boot2docker ip 2>/dev/null"
```