Add note about caching
Add note about caching

CHH/heroku-buildpack-php,mraymond/heroku-buildpack-php,Scalingo/php-buildpack,nsg/dokku-buildpack-picocms,bobmaerten/dokku-buildpack-php,cachethq/cachet-buildpack,stof/heroku-buildpack-php,mraymond/heroku-buildpack-php,stof/heroku-buildpack-php,OKAMca/heroku-buildpack-php,penciu/apache,CHH/heroku-buildpack-php,AlphaStaxLLC/heroku-buildpack-php-custom,OKAMca/heroku-buildpack-php,stof/heroku-buildpack-php,jstacoder/heroku-buildpack-php-1,CHH/heroku-buildpack-php,bobmaerten/dokku-buildpack-php,Jonatasmz/php-buildpack,briankilgore/heroku-buildpack-php-prod,nsg/dokku-buildpack-picocms,pierredup/packager-buildpack-php,Scalingo/php-buildpack,AlphaStaxLLC/heroku-buildpack-php-custom,OKAMca/heroku-buildpack-php,penciu/apache,pierredup/packager-buildpack-php,penciu/apache,AlphaStaxLLC/heroku-buildpack-php-custom,Jonatasmz/php-buildpack,ryosuzuki/php-buildpack,Scalingo/php-buildpack,ryosuzuki/php-buildpack,jstacoder/heroku-buildpack-php-1