Create .gitignore definition

[Mandera]

I thought .git/exclude and .gitignore were interchangeable when I decided to go with .git/exclude

Later learned that .git folder isn't versioned! So let's move this to .gitignore:

generalpackager/generalpackager/api/shared/files/definitions/git_exclude.py

Lines 2 to 11 in bd361ec

	from generalpackager.api.shared.files.file import File
	class GitExcludeFile(File):
	_relative_path = ".git/info/exclude"
	is_file = True
	aesthetic = True
	def _generate(self):
	return "\n".join(self.packager.git_exclude_lines)

And also include

• Add .gitignore generalimport#21