Clarify commit_author input option (#315)

* Clarify `commit_author` input option

* Update README.md

---------

Co-authored-by: Stefan Zweifel <stefanzweifel@users.noreply.github.com>

Author: npanuhin

README.md

@@ -82,7 +82,7 @@ The following is an extended example with all available options.
     # Optional commit user and author settings
     commit_user_name: My GitHub Actions Bot # defaults to "github-actions[bot]"
     commit_user_email: my-github-actions-bot@example.org # defaults to "41898282+github-actions[bot]@users.noreply.github.com"
-    commit_author: Author <actions@github.com> # defaults to author of the commit that triggered the run
+    commit_author: Author <actions@github.com> # defaults to "username <username@users.noreply.github.com>", where "username" belongs to the author of the commit that triggered the run
 
     # Optional. Tag name being created in the local repository and 
     # pushed to remote repository and defined branch.
@@ -353,6 +353,8 @@ If you would like to use this Action to create a commit using [`--amend`](https:
 First, you need to extract the previous commit message by using `git log -1 --pretty=%s`.
 Then you need to provide this last commit message to the Action through the `commit_message` input option.
 
+By default, the commit author is changed to `username <username@users.noreply.github.com>`, where `username` is the name of the user who triggered the workflow (The [`github.actor`](https://docs.github.com/en/actions/learn-github-actions/contexts#github-context) context is used here). If you want to preserve the name and email of the original author, you must extract them from the last commit and provide them to the Action through the `commit_author` input option.
+
 Finally, you have to use `push_options: '--force'` to overwrite the git history on the GitHub remote repository. (git-auto-commit will not do a `git-rebase` for you!)
 
 The steps in your workflow might look like this:
@@ -366,13 +368,15 @@ The steps in your workflow might look like this:
 # Other steps in your workflow to trigger a changed file
 
 - name: Get last commit message
-  id: last-commit-message
+  id: last-commit
   run: |
-    echo "msg=$(git log -1 --pretty=%s)" >> $GITHUB_OUTPUT
+    echo "message=$(git log -1 --pretty=%s)" >> $GITHUB_OUTPUT
+    echo "author=$(git log -1 --pretty=\"%an <%ae>\")" >> $GITHUB_OUTPUT
 
 - uses: stefanzweifel/git-auto-commit-action@v5
   with:
-    commit_message: ${{ steps.last-commit-message.outputs.msg }}
+    commit_author: ${{ steps.last-commit.outputs.author }}
+    commit_message: ${{ steps.last-commit.outputs.message }}
     commit_options: '--amend --no-edit'
     push_options: '--force'
     skip_fetch: true