Add an entry to an existing .gitignore file.
If the .gitignore file doesn't exist, or if the entry is already present, no changes will be made.
The directory containing the .gitignore file.
The entry to add to the .gitignore file.
Add an entry to an existing .gitignore file.
If the .gitignore file doesn't exist, or if the entry is already present, no changes will be made.