Add php-compat-info

Def a good one to include - I use this list pretty often to (re)find tools that I use.
This is a tool I've benefitted from multiple times.

Author: mallardduck

README.md

@@ -34,6 +34,7 @@ Tools to report issues in code that are or lead to bugs.
 * [PHP Assumption](https://github.com/rskuipers/php-assumptions.git) - Finds <a href="http://rskuipers.com/entry/from-assumptions-to-assertions">weak assumptions</a> in the code, suggest to turn them into stronger validations.
 * [PhpCodeAnalyzer](https://github.com/wapmorgan/PhpCodeAnalyzer.git) - Finds usage of non-built-in extensions.
 * [PHPCodeFixer](https://github.com/wapmorgan/PhpCodeFixer) -  Finds usage of deprecated functions, variables and ini directives.
+* [php-compat-info](https://github.com/llaville/php-compat-info) - Find out the minimum version and the extensions required for a piece of code to run.
 * [php7mar](https://github.com/Alexia/php7mar) - PHP 7 Migration Assistant Report.
 * [phpcallgraph](http://phpcallgraph.sourceforge.net/) - Generate static call graphs. Such a graph visualizes the call dependencies among methods or functions of an application..
 * [PHPCPD](https://github.com/sebastianbergmann/phpcpd) - Spots copy/pasted code, and help enforcing DRY rule.