Document and improve default proxy port

[roobre]

When attempting to fault inject a service listening on port 8080, the disruptor fails with the following message:

ERRO[0006] GoError: error injecting fault: error invoking agent: command terminated with exit code 1
the DestinationPort and RedirectPort must be different

We should research whether this can be avoided, and if it cannot, document the behavior and the solution (specify a different port) on a troubleshooting section.

### Tasks
- [ ] Check if this port can be autodetected by the injector
- [ ] Change the default port to a less commonly-used one and document the workaround