v0.5.6 — Updating guidance (docs)

Docs-only release (no code changes vs v0.5.5).

Adds an Updating section to the README (English + German): after a HACS update, redownload → restart Home Assistant, because new release entities only appear after the restart. A missing entity right after an update is almost always "updated in HACS, but HA not restarted yet" rather than a bug.

Shipped as its own release so the guidance shows up in the HACS-rendered README of the installed tag.