Remove & ignore .DS_Store

[infotexture]

The macOS Desktop Services Store file .DS_Store should not be included in Git repositories.

This pull request removes the hidden file from the repository and adds a .gitignore file to ensure that any future changes do not re-add the file.

For more information, see Ignoring Files:

Often, you’ll have a class of files that you don’t want Git to automatically add or even show you as being untracked. These are generally automatically generated files such as log files or files produced by your build system. In such cases, you can create a file listing patterns to match them named .gitignore.