Describe current behavior on the cache interface

src/CacheInterface.php

@@ -2,12 +2,33 @@
 
 namespace React\Cache;
 
+use React\Promise\PromiseInterface;
+
 interface CacheInterface
 {
-    // @return React\Promise\PromiseInterface
+    /**
+     * Retrieve an item from the cache, resolves with its value on
+     * success or rejects when no item can be found.
+     *
+     * @param string $key
+     * @return PromiseInterface
+     */
     public function get($key);
 
+    /**
+     * Store an item in the cache.
+     *
+     * @param string $key
+     * @param mixed $value
+     * @return void
+     */
     public function set($key, $value);
 
+    /**
+     * Remove an item from the cache.
+     *
+     * @param string $key
+     * @return void
+     */
     public function remove($key);
 }