Add caution: don't amend pushed commits

Author: HonkingGoose

book/02-git-basics/sections/undoing.asc

@@ -39,6 +39,12 @@ Effectively, it's as if the previous commit never happened, and it won't show up
 The obvious value to amending commits is to make minor improvements to your last commit, without cluttering your repository history with commit messages of the form, ``Oops, forgot to add a file'' or ``Darn, fixing a typo in last commit''.
 ====
 
+[CAUTION]
+====
+Only amend commits that are still local and have not been pushed somewhere.
+Amending previously pushed commits, and force pushing the branch will cause problems for your collaborators.
+====
+
 [[_unstaging]]
 ==== Unstaging a Staged File