sync/shared-config: sync docs folder.

This should allow us to enforce a consistent structure for documentation
across all our repositories.

.github/actions/sync/shared-config.rb

@@ -24,10 +24,12 @@ def git(*args)
   abort "Usage: #{$PROGRAM_NAME} <target_directory_path> <homebrew_repository_path>"
 end
 
+docs = "docs"
 ruby_version = ".ruby-version"
 rubocop_yml = ".rubocop.yml"
 dependabot_yml = ".github/dependabot.yml"
 
+homebrew_docs = homebrew_repository_path/docs
 homebrew_ruby_version =
   (homebrew_repository_path/"Library/Homebrew/vendor/portable-ruby-version").read
                                                                             .chomp
@@ -57,16 +59,22 @@ def git(*args)
 
 puts "Detecting changes…"
 [
+  docs,
   ruby_version,
   rubocop_yml,
   dependabot_yml,
   ".github/workflows/lock-threads.yml",
   ".github/workflows/stale-issues.yml",
-].each do |file|
-  target_path = target_directory_path/file
+].each do |path|
+  target_path = target_directory_path/path
   target_path.dirname.mkpath
 
-  case file
+  case path
+  when docs
+    next unless target_path.exist?
+    next unless target_path.directory?
+
+    FileUtils.cp_r homebrew_docs, target_path
   when ruby_version
     next if custom_ruby_version_repos.include?(repository_name)
 
@@ -83,13 +91,13 @@ def git(*args)
     )
   when dependabot_yml
     next if custom_dependabot_repos.include?(repository_name)
-    next if file == target_path.to_s
+    next if path == target_path.to_s
 
-    FileUtils.cp file, target_path
+    FileUtils.cp path, target_path
   else
-    next if file == target_path.to_s
+    next if path == target_path.to_s
 
-    FileUtils.cp file, target_path
+    FileUtils.cp path, target_path
   end
 end