Update introduction.rst

In my opinion a note or example needs to be added to the command test example to show that the option needs to be prefixed with a double hyphen.
minor #4057 Update introduction.rst (carltondickson)

This PR was submitted for the 2.4 branch but it was merged into the 2.3 branch instead (closes #4057).

Discussion
----------

Update introduction.rst

In my opinion a note or example needs to be added to the command test example to show that the option name needs to be prefixed with a double hyphen.

Admittedly there is a similar example of passing an option to a command at https://github.com/symfony/symfony-docs/blob/2.4/components/console/introduction.rst#calling-an-existing-command but this could easily be missed.

Commits
-------

ddbadc7 Update introduction.rst