add info to docs about static routes

### Prerequisites

- [X] I have checked the [Wiki](https://github.com/AdguardTeam/AdGuardHome/wiki) and [Discussions](https://github.com/AdguardTeam/AdGuardHome/discussions) and found no answer

- [X] I have searched other issues and found no duplicates

- [X] I want to request a feature or enhancement and not ask a question

### The problem

https://github.com/AdguardTeam/AdGuardHome/wiki/DHCP
is missing an important example on how to add static routes

### Proposed solution

more or less the example would be:
```
- generate hex on https://www.medo64.com/2018/01/configuring-classless-static-route-option/
- eg: for 192.168.0/24 via 192.168.1.18 = 0x00C0A8011218C0A800C0A80112
- remove the 0x from the string
- open AdGuardHome.yaml, go to the `dhcp.dhcpv4.options` array field and modify like this:
```
options:
- 121 hex 00C0A8011218C0A800C0A80112
```
- restart adgh
```

### Alternatives considered and additional information

https://www.reddit.com/r/Adguard/comments/jncg3o/dhcp_options_in_adguard_home/