Add retroactive signing to git.md

git.md

@@ -8,7 +8,7 @@ tags: [ linux, programming, git ]
 
 # Fix detached head
 
-From https://stackoverflow.com/a/10229202 :
+From <https://stackoverflow.com/a/10229202>:
 
 ## To Delete Changes
 
@@ -24,3 +24,19 @@ git checkout main
 git pull . temp
 git branch -D temp
 ```
+
+# Retroactively Sign Commits
+
+From <https://webdevstudios.com/2020/05/26/retroactively-sign-git-commits/>:
+
+1.
+   ```
+   git rebase -i HEAD~<number of commits to sign>
+   ```
+
+2. Replace `pick` with `reword`:
+
+   In vim: `:%s/^pick/reword/:wq`
+
+3. Save all commit messages
+4. Force push to remote