[docs] Docker build - ZeroMQ dependency for Jupyter (#8262)

* doc py3-zmq - ZeroMQ bindings for jupyter

#7970 https://github.com/go-gitea/gitea/issues/7970

* rebase Dockerfile to 1.9.x for jupyter

* [docs] external-renderers.en-us.md - use templated variable for version

Co-Authored-By: techknowlogick <matti@mdranta.net>

docs/content/doc/advanced/external-renderers.en-us.md

@@ -28,13 +28,13 @@ In order to get file rendering through external binaries, their associated packa
 If you're using a Docker image, your `Dockerfile` should contain something along this lines:
 
 ```
-FROM gitea/gitea:1.6.0
+FROM gitea/gitea:{{< version >}}
 [...]
 
 COPY custom/app.ini /data/gitea/conf/app.ini
 [...]
 
-RUN apk --no-cache add asciidoctor freetype freetype-dev gcc g++ libpng python-dev py-pip python3-dev py3-pip
+RUN apk --no-cache add asciidoctor freetype freetype-dev gcc g++ libpng python-dev py-pip python3-dev py3-pip py3-zmq
 # install any other package you need for your external renderers
 
 RUN pip3 install --upgrade pip