docs: add GitHub Pages documentation deployment workflow

- Create GitHub Actions workflow for deploying documentation to GitHub Pages
- Update README.md with documentation badge and link
- Add missing gem dependency in docs/Gemfile
- Configure Jekyll build and deployment process

docs/Gemfile

@@ -10,4 +10,8 @@ gem "jekyll-seo-tag"
 platforms :mingw, :x64_mingw, :mswin, :jruby do
   gem "tzinfo", ">= 1"
   gem "tzinfo-data"
-end 
+end
+
+# Lock `http_parser.rb` gem to `v0.6.x` on JRuby builds since newer versions of the gem
+# do not have a Java counterpart.
+gem "http_parser.rb", "~> 0.6.0", :platforms => [:jruby]