enhance: Add comprehensive .gitignore for deb-mock project

- Add mock-specific build artifacts (chroot/, mock-*, mockroot/)
- Include package build files (*.deb, *.changes, *.buildinfo)
- Add development tools (.coverage, .pytest_cache, .tox)
- Include system files (.DS_Store, Thumbs.db, ._*)
- Add temporary and backup files (*.tmp, *.bak, *.backup)
- Include local configuration overrides (config.local.yaml, .env.local)
- Add test artifacts and documentation builds
- Comprehensive coverage for Python build system project

This ensures build artifacts, chroot environments, and development
tools are properly ignored in version control.

docs/jekyll-theme-slate.gemspec

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+Gem::Specification.new do |s|
+  s.name          = "jekyll-theme-slate"
+  s.version       = "0.2.0"
+  s.license       = "CC0-1.0"
+  s.authors       = ["Jason Costello", "GitHub, Inc."]
+  s.email         = ["opensource+jekyll-theme-slate@github.com"]
+  s.homepage      = "https://github.com/pages-themes/slate"
+  s.summary       = "Slate is a Jekyll theme for GitHub Pages"
+
+  s.files         = `git ls-files -z`.split("\x0").select do |f|
+    f.match(%r{^((_includes|_layouts|_sass|assets)/|(LICENSE|README)((\.(txt|md|markdown)|$)))}i)
+  end
+
+  s.required_ruby_version = ">= 2.4.0"
+
+  s.platform = Gem::Platform::RUBY
+  s.add_runtime_dependency "jekyll", "> 3.5", "< 5.0"
+  s.add_runtime_dependency "jekyll-seo-tag", "~> 2.0"
+  s.add_development_dependency "html-proofer", "~> 3.0"
+  s.add_development_dependency "rubocop-github", "~> 0.16"
+  s.add_development_dependency "w3c_validators", "~> 1.3"
+end