Updated Docker (markdown)

Docker.md

@@ -1,3 +1,31 @@
+## Building custom Docker image
+
+This is only for developers. For normal users, do not add these options, just start with `docker compose up -d`
+
+Alpine Linux does not work properly with current Meteor 2 based WeKan. Ubuntu works, and has newest security fixes.
+
+Only amd64 currently works. Currently used Node.js 14.x segfaults at arm64 and s390x. Only Node.js 14.x is compatible with current version of Meteor 2 based WeKan. Trying to upgrade is in progress #5475
+
+Dockerfile is at https://raw.githubusercontent.com/wekan/wekan/main/Dockerfile
+
+For building custom image, and then running it, uncomment these lines:
+
+https://github.com/wekan/wekan/blob/main/docker-compose.yml#L144-L146
+
+Then modify ROOT_URL, etc settings as needed, see https://github.com/wekan/wekan/wiki/Settings
+
+Start WeKan with custom built Dockerfile with this command:
+```
+docker compose up -d --build
+```
+If you like to only build Dockerfile:
+```
+docker build .
+```
+You can also push your image to some Docker registry, like here it's done for WeKan:
+
+https://github.com/wekan/wekan/blob/main/releases/docker-push-wekan.sh
+
 ## Docker Containers
 
 - [GitHub](https://github.com/wekan/wekan/pkgs/container/wekan)