clarified the HEAD~2 root commit issue and suggested using --root or creating an initial commit (bregman-arie#10569)

Author: djeada

topics/git/solutions/squashing_commits.md

@@ -1,24 +1,27 @@
 ## Git - Squashing Commits - Solution
 
-
-1. In a git repository, create a new file with the content "Mario" and commit the change
+1. In a git repository, create a new file with the content "Mario" and commit the change:
 
 ```
+echo "Mario" > new_file
 git add new_file
-echo "Mario" -> new_file
-git commit -a -m "New file"
+git commit -m "New file"
 ```
 
-2. Make change to the content of the file you just created so the content is "Mario & Luigi" and create another commit
+2. Make a change to the content of the file you just created so it becomes "Mario & Luigi," then create another commit:
 
 ```
 echo "Mario & Luigi" > new_file
 git commit -a -m "Added Luigi"
 ```
 
-3. Verify you have two separate commits - `git log`
+3. Verify you have two separate commits by running:
+
+```
+git log
+```
 
-4. Squash the two commits you've created into one commit
+4. Squash the two commits you've created into one commit:
 
 ```
 git rebase -i HEAD~2
@@ -31,19 +34,25 @@ pick 5412076 New file
 pick 4016808 Added Luigi
 ```
 
-Change `pick` to `squash`
-
+Change `pick` to `squash`:
 
 ```
 pick 5412076 New file
 squash 4016808 Added Luigi
 ```
 
-Save it and provide a commit message for the squashed commit
+Save it and provide a commit message for the squashed commit.
+
+> **Note**: If running `git rebase -i HEAD~2` returns a fatal error (e.g., "invalid upstream 'HEAD~2'"), that usually means your second commit is actually the root commit and there's no valid parent before it. In that case, you can either:
+> * Use `git rebase -i --root` to allow rewriting the root commit, **or**
+> * Create an initial commit before these two commits so that `HEAD~2` points to valid commits.
 
 ### After you complete the exercise
 
-Answer the following:
+**Answer the following:**
+
+* **What is the reason for squashing commits?**  
+  History becomes cleaner and it's easier to track changes without many small commits like "removed a character," for example.
 
-* What is the reason for squashing commits? - history becomes cleaner and it's easier to track changes without commit like "removed a character" for example. 
-* Is it possible to squash more than 2 commits? - yes
+* **Is it possible to squash more than 2 commits?**  
+  Yes.