Fix grammar in openwrt-zarhus docs

[m-iwanicki]

e.g.: https://github.com/zarhus/openwrt-zarhus/blob/protectli-v24.10.1/docs/building.md

• OpenWRT -> OpenWrt
• step by step -> step-by-step
• WiFi -> Wi-Fi

And possibly others. Go through docs with spellchecker, grammarly, LanguageTool or similar and fix all issues.