Add initial setup instructions.

README.md

@@ -44,3 +44,33 @@ Two things that you need to do that are beyond the scope of this project:
 * Cache your overleaf credentials, it is not possible to use SSH for overleaf.
 * Run the script periodically, e.g. every minute or before and after each change
   you want to make.
+
+## Initial setup
+
+Overleaf does some strange things with git. E.g. it deletes all the history
+when importing a project, but creates a history when creating a new project.
+
+Therefore some special instructions need to be followed to initially setup
+the linked projects.
+
+### Setup from existing GitLab repository
+
+First create a new blank project. Do not import a project. Choose 'git' in the
+'Sync' menu and copy the url (but note the `git clone` part). It should look
+like https://git.overleaf.com/5efb2cbe8306d30001f4cba8.
+
+```shell script
+git clone git@gitlab.astro-wise.org:buddel/testlatex2.git
+cd testlatex2
+git remote rename origin gitlab
+git remote add overleaf https://git.overleaf.com/5efb2cbe8306d30001f4cba8
+git fetch overleaf
+git merge -X ours overleaf/master
+git push overleaf master
+git push gitlab master
+```
+
+### Setup from existing Overleaf repository
+This is simpler, just create an empty project on GitLab (that is, do not
+initialize with a readme), clone the Overleaf repository like usual, add
+the GitLab remote and push there.