minor #676 Simplified the README instructions (javiereguiluz)
minor #676 Simplified the README instructions (javiereguiluz)

This PR was squashed before being merged into the master branch (closes #676).

Discussion
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Simplified the README instructions

This is needed because we're moving away from the Symfony Installer and we'll use Composer's create-project from now on.

Commits
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aeece08 Simplified the README instructions

Codeception/symfony-demo,javiereguiluz/symfony-demo,TomasVotruba/symfony-demo,bocharsky-bw/symfony-demo,voronkovich/symfony-demo,symfony/symfony-demo,bocharsky-bw/symfony-demo,symfony/symfony-demo,javiereguiluz/symfony-demo,symfony/symfony-demo,Codeception/symfony-demo,bocharsky-bw/symfony-demo,javiereguiluz/symfony-demo,voronkovich/symfony-demo,voronkovich/symfony-demo,yceruto/symfony-demo,TomasVotruba/symfony-demo,Codeception/symfony-demo,yceruto/symfony-demo,TomasVotruba/symfony-demo,yceruto/symfony-demo