You could set up a workflow that emails the document uploader (Created By) that starts when an item is modified. Below is how to accomplish this.

1. Create a new workflow on the library.
2, Go to the Workflow Settings.
3. Go to the Workflow Options section.
4. Set the “Start when items are modified” option to “Yes”.
5. Click the Save button.
6.. Add and configure a “Send notification” action to the workflow.

• To the right of the “To” field, click on the Browse button.
• Expand the Lookup section.
• Under the Item Properties, select “Created By” and click the Add button to add it to the Selections.
• Click the OK button,
• Configure the rest of the “Send notification” action (i.e. Subject, email body, etc.).
• Click the Save button.

7. Save and/or Publish the workflow.

Publishing the workflow with these steps will trigger the workflow to send an email to the document uploader when any change is made to the uploaded document.