add multi repo notes

Author: arch

docs/app/docs/user-guide/developer.md

@@ -4,6 +4,17 @@
 
 I have only a Winows KVM with gpu passthrough for testing, therefore i do not know very much about the development of python applications on Windows. For testing i use the `build_and_deploy.bat` script from the repository root directory.
 
+## Pushing to multiple git repositories
+
+Use the following to add several pushurls to your origin:
+
+```bash
+git remote set-url --add --push origin git://original/repo.git
+git remote set-url --add --push origin git://another/repo.git
+```
+
+Now you can use `git push` to push changes to multiple git repositories.
+
 ## GitHub Release API
 
 Get all release information: