[ci skip] Add code example for MailHelper#block_format documentation

actionmailer/lib/action_mailer/mail_helper.rb

@@ -4,7 +4,17 @@ module ActionMailer
   # attachments list.
   module MailHelper
     # Take the text and format it, indented two spaces for each line, and
-    # wrapped at 72 columns.
+    # wrapped at 72 columns:
+    #
+    #   text = <<-TEXT
+    #     This is
+    #     the      paragraph.
+    #
+    #     * item1 * item2
+    #   TEXT
+    #
+    #   block_format text
+    #   # => "  This is the paragraph.\n\n  * item1\n  * item2\n"
     def block_format(text)
       formatted = text.split(/\n\r?\n/).collect { |paragraph|
         format_paragraph(paragraph)