To add a custom git commit message, create a file at ~/.gitmessage detailing what you want the git commit to say. A good template to start with is:
## if applied, this commit will...
## [Close/Fix/Resolve/Add/Remove/Update/Refactor/Document] [issue #id] [summary]
## Why is it necessary? (Bug fix, feature, improvements?)
-
## How does the change address the issue?
-
## What side effects does this change have?
-
Then, run the following command to ensure that the template is used:
git config --global commit.template ~/.gitmessage
Be sure to not use git commit -m when you are committing. A normal git commit command will use the template properly.