Add documentation_uri to gemspec

Author: sue445

gem/go_gem.gemspec

@@ -17,6 +17,7 @@ Gem::Specification.new do |spec|
   spec.metadata["homepage_uri"] = spec.homepage
   spec.metadata["source_code_uri"] = spec.homepage
   spec.metadata["changelog_uri"] = "#{spec.homepage}/blob/main/CHANGELOG.md"
+  spec.metadata["documentation_uri"] = "https://sue445.github.io/go-gem-wrapper/"
   spec.metadata["rubygems_mfa_required"] = "true"
 
   # Specify which files should be added to the gem when it is released.