[Feature]: Documentation: provide comprehensive "install" instructions

### Pre-flight checklist

- [x] I searched existing issues and the [Roadmap](https://github.com/AprilNEA/OpenLogi#roadmap), and this isn't already tracked.

### Problem / motivation

The install instruction currently consists of this sentence: "Quit Logi Options+ first: the two applications fight over HID++ access, and only one can own a given receiver at a time."

This is too short. Why should quitting be enough when Options+ has permission to run in the background and several [other permissions](https://support.logi.com/hc/en-gb/articles/1500005514962-Logi-Options-permissions-on-macOS) in place? Wouldn't it be better to toggle off the permissions before using OpenLogi? Do you consider Options+ a software that can still be used in addition or next to OpenLogi?

### Proposed solution

Describe potential conflicts with other HID customizer applications in more than one sentence. Before even installing OpenLogi, users should learn what to do with Options+, the permissions, and other tools like Karabiner-Elements.

### Alternatives considered

_No response_

### Related area(s)

- [ ] GUI
- [ ] CLI
- [ ] Button actions / remapping
- [ ] DPI
- [ ] SmartShift
- [ ] Per-application profiles
- [ ] Configuration (TOML)
- [ ] Auto-update
- [x] Other

### Additional context

_No response_

Start with the existing install instruction and review the linked Logi Options permissions guidance. Document what users should do with Options+, its background permissions, and other HID customizer applications such as Karabiner-Elements, including whether they can be used alongside OpenLogi; the installation documentation is complete when these conflicts and steps are explained clearly.

Written by the indexing model from the issue text.