Update to Readme.md

Note incompatibility with PHP 5.5 and higher
Adds client management interface. Requires migration.
API implementation for private packs. Cache should also clear immediately now when changes are made in Solder. No more wait time!
Got rid of statistics link. Its never coming. :)
Now checks to make sure files exist. Fixes the bug where you get an MD5 even though the file doesnt exist.
Removed composer file and changed name in license file