- `rails initializers --help` should show description set by `desc`
See railties/lib/rails/command/base.rb:27
- Fix `rails dev:cache --help`
```
Traceback (most recent call last):
10: from bin/rails:4:in `<main>'
9: from bin/rails:4:in `require'
8: from /work/rails/railties/lib/rails/commands.rb:18:in `<top (required)>'
7: from /work/rails/railties/lib/rails/command.rb:46:in `invoke'
6: from /work/rails/railties/lib/rails/command/base.rb:65:in `perform'
5: from /home/vagrant/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/thor-0.20.0/lib/thor.rb:387:in `dispatch'
4: from /home/vagrant/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/thor-0.20.0/lib/thor/invocation.rb:126:in `invoke_command'
3: from /home/vagrant/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/thor-0.20.0/lib/thor/command.rb:27:in `run'
2: from /work/rails/railties/lib/rails/command/base.rb:150:in `help'
1: from /home/vagrant/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/thor-0.20.0/lib/thor.rb:170:in `command_help'
/home/vagrant/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0/gems/thor-0.20.0/lib/thor/base.rb:497:in `handle_no_command_error': Could not find command "dev". (Thor::UndefinedCommandError)
```
Context https://github.com/rails/rails/pull/33694#issuecomment-415127304
Would be great to set a description to other commands.
