Add simple usage examples

Author: o-p

README.md

@@ -1 +1,21 @@
 # An unofficial PHP implementation of JsonLogic
+
+### Usage
+
+- For an one-time logic to data use case, the `apply` function is enough:
+
+    ```php
+    echo \JsonLogic\JsonLogic::apply($rule, $data);
+    ```
+
+- For a rule runs tons times, e.g. find matched records in daily logs:
+
+    ```php
+    $rule = \JsonLogic\JsonLogic::rule($rule);
+
+    var_dump(
+        array_filter($logs, function ($log) use ($rule) {
+            return $rule->process($log);
+        })
+    );
+    ```