Improve instructions

README.md

 # gitremotesync
 
-Sync the master branches of the local repository and all remotes.
+Sync the master branches of the local repository and all remotes.
\ No newline at end of file
+
+E.g. running this in a git repository with these remotes, will synchronize
+three repositories:
+```shell script
+$ git remote -v
+github  git@github.com:hugobuddel/testlatex2.git (fetch)
+github  git@github.com:hugobuddel/testlatex2.git (push)
+gitlab  git@gitlab.astro-wise.org:buddel/testlatex2.git (fetch)
+gitlab  git@gitlab.astro-wise.org:buddel/testlatex2.git (push)
+overleaf        https://git.overleaf.com/5ef9e60ebb7def000199c1c5 (fetch)
+overleaf        https://git.overleaf.com/5ef9e60ebb7def000199c1c5 (push)
+```
+
+These projects will be synchronized:
+* https://www.overleaf.com/project/5ef9e60ebb7def000199c1c5
+* https://gitlab.astro-wise.org/buddel/testlatex2
+* https://github.com/hugobuddel/testlatex2
+
+Any change to master of one of these projects will propagate to the others.
+This will allow seamless collaboration through overleaf, github and/or gitlab.
+
+Collaborators who prefer to use merge/pull requests can do so through gitlab
+or github. These changes will seem like an extremely fast typer to the
+collaborators that are using overleaf. Vice versa, overleaf users appear
+as people who create many commits to the gitlab/github users.
+
+To run this script, clone one of the repositories,
+add the other remotes, then run the script.
+```shell script
+git clone git@gitlab.astro-wise.org:buddel/gitremotesync.git
+git clone git@gitlab.astro-wise.org:buddel/testlatex2.git
+cd testlatex2
+git init
+git remote rename origin gitlab
+git remote add overleaf https://git.overleaf.com/5ef9e60ebb7def000199c1c5
+git remote add github git@github.com:hugobuddel/testlatex2.git
+bash ../gitremotesync/synchronize.sh
+``` 
+
+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.