Added info to docker-compose.yml about newest docker image of newest git commit automatic build.

Thanks to xet7 !

docker-compose.yml

@@ -120,7 +120,10 @@ services:
     # image: quay.io/wekan/wekan:v6.89
     # image: wekanteam/wekan:v6.89
     # b) GitHub Container registry.
+    # b1) Latest release tag:
     image: ghcr.io/wekan/wekan:latest
+    # b2) Newest git commit automatic build:
+    #image: ghcr.io/wekan/wekan:main
     # c) Quay:
     #image: quay.io/wekan/wekan:latest
     # d) Docker Hub: