Readme and contributing info

Hello, in the php-src repository there are few files mentioning the contributing procedure. If I may suggest few improvements and readability cosmetics: https://github.com/php/php-src/pull/2833 What has been changed so far? - PHP installation procedure would be best described at a single entry php.net/install - The README.md includes a brief PHP general description, Git repositories links, PHP installation info, and a link to a CONTRIBUTING.md file - README.GIT-RULES and README.SUBMITTING_PATCH files are joined into an existing CONTRIBUTING.md file - README.WIN32-BUILD-SYSTEM is redundant and removed in favor of the README.md - INSTALL file removed in favor of the main README.md file - windows archive package gets readme.txt attached from README.md In the current PHP-7.x branches there was a practice to generate an installation information from the documentation repository and attached as INSTALL and win32/install.txt files which isn't so anymore with master branch on I believe. Reason for all these refactorings is simplicity for people not used to contributing to php-src repo yet still having all the relevant information in the repo. If possible, can someone please take a look at these or suggest something better? I plan to do some more cosmetic improvements later on also. Thanks. -- Peter Kokot