Updated the README.md

We were missing some important steps in setting up a
vanilla environment.
Remove prior vendor folder
Move PHP's composer to proper directory
Update config to remove spurious warnings
install composer.par directly under IROOT
add version argument to PHP installation
Fix yii2 dependency installation

a prior commit removed the vendor directory that was erroneously added into this
repo, and this commit adds that vendor directory back using the composer
dependency management system
Lock php-yii2 assets to a known-good state
Update PHP read to explain composer usage
Update PHP-yii2 installation
Fix typo
Move Yii2 into properly-named directory
Merge pull request #1274 from hamiltont/fix-php-yii2

PHP: Replace Yii2 source with composer download
Remove phreeze library source code from repository
Download phreeze using composer
Remove lithium source code from our repository
download lithium with composer
Move to lithium from php-lithium
Forgot to use composer in install.sh
Remove bash_profiles