imap-backup.gemspec in imap-backup-1.4.2 vs imap-backup.gemspec in imap-backup-2.0.0.rc1

@@ -13,9 +13,16 @@
   gem.executables   = gem.files.grep(%r{^bin/}).map { |f| File.basename(f) }
   gem.test_files    = gem.files.grep(%r{^spec/})
   gem.require_paths = ["lib"]
   gem.version       = Imap::Backup::VERSION
 
+  gem.post_install_message = <<-MESSAGE.gsub(/^\s{4}/m, "")
+    When upgrading #{gem.name} from version 1.x to 2.x not that the
+    metadata storage method has changed (from flat file to JSON).
+    As a result, on the first run after an upgrade, old backup folders will be
+    **deleted** and a full new backup created.
+  MESSAGE
+
   gem.add_runtime_dependency "rake"
   gem.add_runtime_dependency "highline"
   gem.add_runtime_dependency "mail"
 
   gem.add_development_dependency "codeclimate-test-reporter", "~> 0.4.8"