installation instructions need update

[m4sterbunny]

https://github.com/networq/networq-php/blob/master/README.md

Install instructions -
requires prerequisite:

1. Composer install (windows only or Linux also)?
   need link to https://getcomposer.org/doc/00-intro.md

[joostfaassen]

@m4sterbunny agreed! Can you provide a PR listing prerequisites?