Update profile image wording

README.md

@@ -10,7 +10,7 @@ What better way to submit a talk proposal than via GitHub!
 2. Copy the sample folder `example/` to `your_name-talk_name`
 3. Edit the `README.md` file and type a good description about your talk
    and about yourself
-4. Replace the `profile_picture.jpg` with a picture of yourself that we
+4. Replace the dummy image with a picture of yourself that we
    can use to list you on the speakers page when you are accepted.
 5. Create a pull request of your fork. Consider using the title of your
    talk as the pull request subject, as this makes the list of pull requests