To add custom article submission field:
Files needed to edit:
i. jos_content table in joomla database
ii. root/components/com_content/views/article/tmpl/default.php
iii. root/components/com_content/views/article/tmpl/form.php
iv. root/administrator/components/com_content/models/article.xml
v. root/administrator/components/admin.content.html.php
vi. root/administrator/components/config.xml
vii. root/libraries/joomla/database/table/content.php