Add documentation for working with stacked branches

Author: stefanhaller

docs/README.md

@@ -6,4 +6,5 @@
 * [Keybindings](./keybindings)
 * [Undo/Redo](./Undoing.md)
 * [Searching/Filtering](./Searching.md)
+* [Stacked Branches](./Stacked_Branches.md)
 * [Dev docs](./dev)

docs/Stacked_Branches.md

@@ -0,0 +1,18 @@
+# Working with stacked branches
+
+When working on a large branch it can often be useful to break it down into
+smaller pieces, and it can help to create separate branches for each independent
+chunk of changes. For example, you could have one branch for preparatory
+refactorings, one for backend changes, and one for frontend changes. Those
+branches would then all be stacked onto each other.
+
+Git has support for rebasing such a stack as a whole; you can enable it by
+setting the git config `rebase.updateRfs` to true. If you then rebase the
+topmost branch of the stack, the other ones in the stack will follow. This
+includes interactive rebases, so for example amending a commit in the first
+branch of the stack will "just work" in the sense that it keeps the other
+branches properly stacked onto it.
+
+Lazygit visualizes the invidual branch heads in the stack by marking them with a
+cyan asterisk (or a cyan branch symbol if you are using [nerd
+fonts](Config.md#display-nerd-fonts-icons)).