add readme

Author: lloydzhou

README.md

@@ -0,0 +1,21 @@
+# fcache
+cache to file, using modified time to controll expire.
+
+## Example
+
+```php
+<?php
+include "fcache.php";
+
+$cache = fcache('./', 1);
+
+// set cache
+// will see file named "name-b068931cc450442b63f5b3d276ea4297" with content 's:5:"value";'
+$cache('name', 'value');
+// get cache
+echo $cache('name');
+sleep(1);
+// cache expire
+echo $cache('name') ?: "\r\ncan not get cache!";
+
+```