add an initial Gemspec, Gemfile, and lockfile

Gemfile

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+#source "https://rubygems.org"
+gemspec

Gemfile.lock

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+PATH
+  remote: .
+  specs:
+    atomic-red-team (1.0)
+
+GEM
+  specs:
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  atomic-red-team!
+
+BUNDLED WITH
+   1.13.7

atomic-red-team.gemspec

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+# Describe your gem and declare its dependencies:
+Gem::Specification.new do |s|
+  s.name        = 'atomic-red-team'
+  s.version     = '1.0'
+  s.authors     = ['Red Canary', 'Casey Smith', 'Mike Haag']
+  s.email       = ['it@redcanary.com', 'casey.smith@redcanary.com', 'mike.haag@redcanary.com']
+  s.summary     = 'Small, highly portable, community developed detection tests mapped to ATT&CK.'
+  s.license     = "MIT"
+  s.homepage    = "https://redcanary.com/atomic-red-team"
+  s.files       = %w(atomic-red-team.gemspec) + Dir['{atomic_red_team}/**/*', '*.md', 'bin/*']
+  s.test_files  = Dir['spec/**/*']
+  s.require_paths = %w(atomic_red_team)
+end