use fqin for container images (#125)

It's generally considered a better practice and it's more portable allowing podman to work without having to modify the name.

Reviewed-on: https://gitea.com/gitea/docs/pulls/125
Reviewed-by: Lunny Xiao <[email protected]>
Co-authored-by: TheFox0x7 <[email protected]>
Co-committed-by: TheFox0x7 <[email protected]>

i18n/zh-cn/docusaurus-plugin-content-docs/current/administration/external-renderers.md

@@ -24,7 +24,7 @@ Gitea 通过外部二进制文件支持自定义文件渲染（例如 Jupyter no
 如果您正在使用 Docker 镜像，则您的 `Dockerfile` 应该包含以下内容：
 
 ```docker
-FROM gitea/gitea:@dockerVersion@
+FROM docker.io/gitea/gitea:@dockerVersion@
 [...]
 
 COPY custom/app.ini /data/gitea/conf/app.ini

i18n/zh-cn/docusaurus-plugin-content-docs/current/administration/reverse-proxies.md

@@ -360,7 +360,7 @@ backend gitea
 
 ```yaml
 gitea:
-  image: gitea/gitea
+  image: docker.io/gitea/gitea
   ...
   labels:
     - "traefik.enable=true"
@@ -376,7 +376,7 @@ gitea:
 
 ```yaml
 gitea:
-  image: gitea/gitea
+  image: docker.io/gitea/gitea
   ...
   labels:
     - "traefik.enable=true"