Update Swift.gitignore

[mirhadiali]

Reasons for making this change:

Added DS_Store (Desktop Services_Store) file, a macOS file that is created by Finder in every folder to hold the user's folder view preferences. This file always has changes when committing to git which is too irritating so it should be in gitignore.

TODO

Links to documentation supporting these rule changes:

TODO

If this is a new template:

• Link to application or project’s homepage: TODO