Contribute to ERPNext Core - add a custom field

Hi. I revised the Chart of Accounts Importer to allow use of Account Number as parent account in the uploaded csv file.

I added a checkbox for Use Account Number as Parent Account in the Chart of Accounts Importer form using the Desktop’s Customize Form tool. This changed the chart_of_accounts_importer.json file.

As the screen shots of the pull request shows, it is doing its job on my local setup.

For the pull request, I see that there is a travis error during installation. I think this is caused by the new field use_account_number_as_parent.

Does adding a custom field in an existing erpnext form require a patch, if we are contributing to the source code?

How do I make contributions to the source code which make changes to the DocType structure?