update impossibe : platform key is required

[alka79]

Hi, I tried to update and could not, with a red message about a missing platform key.

Along the versions of ESPHome, there was this breaking change https://github.com/esphome/esphome/pull/6459

now - platform: esphome is required for ota update.

Maybe update the yaml example config to reflect this. Not a big deal. Thanks