Add Easypanel as a Docker deployment option

[Ahson-Shaikh]

Hi — this is Ahson Shaikh, DevOps Engineer at Easypanel. Easypanel is a self-hosted Docker deployment platform, and CodiMD has a one-click deployment template there: https://easypanel.io/templates/hackmdio

I noticed the Docker deployment docs live on a hosted HackMD note rather than in this repo, so I can't open a PR the usual way. Would you be open to adding a mention there, or pointing me to how I could contribute to that note directly?

Deploy-tested the template before opening this - booted clean.