docker: update link to Docker Hub and add info for gogs-rpi

[CI SKIP]

docker/README.md

@@ -2,10 +2,12 @@
 
 ![Docker pulls](https://img.shields.io/docker/pulls/gogs/gogs?logo=docker&style=for-the-badge) ![Docker image size](https://img.shields.io/microbadger/image-size/gogs/gogs?logo=docker&style=for-the-badge)
 
-Visit [Docker Cloud](https://cloud.docker.com/u/gogs/repository/docker/gogs/gogs) see all available images and tags.
+Visit [Docker Hub](https://hub.docker.com/repository/docker/gogs) see all available images and tags.
 
 ## Usage
 
+ℹ️ Please use `gogs/gogs-rpi` if you're using Raspberry Pis!
+
 To keep your data out of Docker container, we do a volume (`/var/gogs` -> `/data`) here, and you can change it based on your situation.
 
 ```sh