Added rebase instructions

.SETUP_DOTFILES.md

@@ -47,6 +47,17 @@ config commit -m "Add bashrc"
 config push
 ```
 
+## Performing a rebase after changes in the main repo
+
+After you've made some changes in the main repo the machine specific repositories need to be rebased on top of main:
+
+```bash
+config checkout machine-repo
+config rebase main
+config log --all # check if everything is ok because we need a force push after
+config push -f origin machine-repo
+```
+
 ## Installing your dotfiles onto a new system (or migrate to this setup)
 
 ----------