Expand Readme

Author: ingwinlu

README.md

@@ -15,13 +15,26 @@ Or a simple `docker-compose up` (you might want to edit the source of
 the image in).
 
 Add a user:
-``docker exec git_server sh add_git_user.sh winlu "`cat ~/.ssh/id_rsa.pub`"``
+```
+docker exec git_server sh add_git_user.sh winlu "`cat ~/.ssh/id_rsa.pub`"
+```
 
 Initialize a repo:
-`ssh localhost -p 1234 "init my_repo.git"`
+```
+ssh localhost -p 1234 "init my_repo.git"
+```
 
 Add remote to your git repository:
-`git remote add docker_git_server ssh://localhost:1234/~/my_repo.git`
+```
+git remote add docker_git_server ssh://localhost:1234/~/my_repo.git
+```
 
 And push:
-`git push docker_git_server --set-upstream master`
+```
+git push docker_git_server --set-upstream master
+```
+
+## Persistence
+It is recommended to use a docker volume for persistence because of
+file permission issues. All data (setup users, repositories, ssh server keys)
+is kept alive during container removal/upgrade.