Update ADD_TO_EXISTING_PACKAGE.md

Author: sverhoeven

ADD_TO_EXISTING_PACKAGE.md

@@ -21,7 +21,7 @@ $ git merge existing_code/<BRANCH> --allow-unrelated-histories
 ```
 
 4. The previous step will likely result in several merge conflicts. Solve the conflicts by editing the files.
-5. Add all the files to GitHub:
+5. Once all conflicts have been resolved then add all the files to GitHub:
 ```shell
 $ git add --all
 $ git commit -m "Merged existing code with code generated by cookiecutter"