Outdated method of specifying path to siad in README

[starius]

README.md says:

If it's outside of your path, provide its location using the -siad flag. For all flags, see sia-antfarm -h.

Option -siad doesn't work. sia-antfarm -h prints the following:

Usage of sia-antfarm:
  -config string
        path to the sia-antfarm configuration file (default "config.json")

The option seems to be replaced with a setting in the config file:

https://github.com/NebulousLabs/Sia-Ant-Farm/blob/ccf3055e3a9f91ee4cc6a35ef92ea7da78dfdced/sia-antfarm/ant.go#L189