add php-doc for ellipsis

lib/helper.php

@@ -713,7 +713,13 @@ class OC_Helper {
 		return false;
 	}
 
-
+	/**
+	 * Shortens str to maxlen by replacing characters in the middle with '...', eg.
+	 * ellipsis('a very long string with lots of useless info to make a better example', 14) becomes 'a very ...example'
+	 * @param string $str the string
+	 * @param string $maxlen the maximum length of the result
+	 * @return string with at most maxlen characters
+	 */
 	public static function ellipsis($str, $maxlen) {
 		if (strlen($str) > $maxlen) {
 			$characters = floor($maxlen / 2);