How to install and run? Composer errors.

[MichaelJCole]

Ran php bootstrap.php and got this error:

PHP Warning:  require(vendor/autoload.php): failed to open stream: No such file or directory in /home/michael/scm/github2gitlab/bootstrap.php on line 3
PHP Fatal error:  require(): Failed opening required 'vendor/autoload.php' (include_path='.:/usr/share/php:/usr/share/pear') in /home/michael/scm/github2gitlab/bootstrap.php on line 3

I installed composer from here: https://getcomposer.org/download/

☀  php composer.phar install                                         Mod master
Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

Did I miss something?