update with HACS store availability

[artmg]

It appears that this integration now shows up in the HACS store - possibly because of the new topics on the repo. I need to double-check it shows up fine, and updated the ReadMe instructions accordingly. Maybe add a screenshot, or links to HACS instructions?

Also, the Warmup branding needs adding https://hacs.xyz/docs/publish/integration/#home-assistant-brands

[rct]

FYI - 12_ hours later, I'm not seeing warmup show up in my HACS instances.

Checked https://hacs.xyz/docs/basic/updates/

• If a component isn't installed it could take 25+ hours for it to show up as HACS only checks every 25 hours or on startup.
• Installed components are check every 2 hours. I should have seen the update to 3.22 by now I think.

[artmg]

I have just installed a fresh test instance and added HACS, and it's not showing up for me yet. If it doesn't appear by whatever magic it did last time, we can follow the steps to request inclusion https://hacs.xyz/docs/publish/include

for now let's see where patience gets us 😄

[artmg]

Branding logo and icon in progress home-assistant/brands#4233

[artmg]

Our PR has been accepted and our repository is now in HACS/Default 🥳

We can update the README with new simpler instructions, and start using 'my link' buttons (see example)

[artmg]

README and detailed instructions now in master