Sync notifications and troubleshooting guides (#998)

* Add help articles

* Broadcast sync messages as notifications

* Lint fixes

* more lint fixes

* Remove redundant code

test/models/help/article_test.rb

@@ -0,0 +1,21 @@
+require "test_helper"
+
+class Help::ArticleTest < ActiveSupport::TestCase
+  include ActiveJob::TestHelper
+
+  setup do
+    Help::Article.stubs(:root_path).returns(Rails.root.join("test", "fixtures", "files"))
+  end
+
+  test "returns nil if article not found" do
+    assert_nil Help::Article.find("missing")
+  end
+
+  test "find and renders markdown article" do
+    article = Help::Article.find("placeholder")
+
+    assert_equal "Placeholder", article.title
+    assert_equal "Test help article", article.content
+    assert_equal "<p>Test help article</p>\n", article.html
+  end
+end