Update --help to mention that --migrate is still in beta

src/invidious.cr

@@ -103,7 +103,7 @@ Kemal.config.extra_options do |parser|
     puts SOFTWARE.to_pretty_json
     exit
   end
-  parser.on("--migrate", "Run any migrations") do
+  parser.on("--migrate", "Run any migrations (beta, use at your own risk!!") do
     Invidious::Database::Migrator.new(PG_DB).migrate
     exit
   end