Fix broken Home Assistant doc link in README

[sneezegray]

The link to the Home Assistant integration (doc/hass.md) pointed to a non-existent file. Fixed to point to the correct documentation page: https://opensoho.github.io/docs/home-assistant/

[sneezegray]

I'd like to contribute more to this project going forward. Are there areas where contributions are particularly welcome, or is there a preferred way to coordinate?

[rubenbe]

There are quite some things:

• Documentation! That is absolutely lacking and out of date.
• The issue you found also shows that opensoho is still lacking a lot of input validation.
• In case you want to contribute features, maybe first open a bug report to discuss.
  Feature wise I think we are nearing what we want for configuration. (famous last words ;) )
  For monitoring I'm considering switching from the REST api towards MQTT integration. Since the latter is way better integrated into HASS.
• I would also want to add "dirty-ing" where the configuration is correctly marked out of date when any record referencing that device is updated.

Thanks @sneezegray for the fix!