Specify that puma gem needs to be installed

[gabriel-cardoso]

Adding this since I got stuck for a few hours trying to understand why puma-dev would not work.

I was trying to use it on a Rails 4 app hence not running on puma already

[bf4]

@gabriel-cardoso the puma gem isn't required.

You don't even need rails to use puma-dev

[tvdeyen]

You don't even need rails to use puma-dev

This is not true:

In a Rails 4 project (where puma is not part of the default Gemfile)

$ grep puma Gemfile.lock
=> 

accessing the project.test host in a browser we get

unexpected exit:
	bash: line 23: exec: puma: not found

adding puma to the Gemfile

$ bundle add puma --group development

helps to make it work.

Probably worth noting that we need puma gem in the Ruby we are currently using.