Update C-git-commands.asc with a new TextEdit command

[pibion]

• [x] I provide my work under the project license.
• [x] I grant such license of my work as is required for the purposes of future print editions to Ben Straub and Scott Chacon.

Changes

• Update C-git-commands.asc with a new TextEdit command

Context

The existing git config instructions for TextEdit on Mac would hang after closing the TextEdit program. The instructions outlined in https://ericasadun.com/2018/07/12/using-textedit-as-your-git-editor/ worked and I propose updating the book with her solution.