When you have your mercurial docker container up and running, these are the steps to create a new repo.
On your server, login to mercurial docker container:
docker exec -it $SSHCONTAINER bash su - hg
Then create your new repo:
mkdir repo mkdir $REPONAME cd $REPONAME hg init hg verify
Add new files and commit:
touch README.md hg addremove HGUSER=your_username_here hg commit -m "First flight" hg update
Then Ctrl+D two times to exit hg user shell and docker exec shell.
Now the repo is available and can be cloned:
hg clone ssh://mycodehosting.example.org/repo/$REPONAME