Added more documentation

types/nodegit/ref-db.d.ts

@@ -1,8 +1,30 @@
 import { Repository } from './repository';
 
 export class Refdb {
+    /**
+     *
+     *
+     * @static
+     * @param {Repository} repo
+     * @returns {Promise<Refdb>}
+     *
+     * @memberof Refdb
+     */
     static open(repo: Repository): Promise<Refdb>;
 
+    /**
+     *
+     *
+     * @returns {number}
+     *
+     * @memberof Refdb
+     */
     compress(): number;
+    /**
+     *
+     *
+     *
+     * @memberof Refdb
+     */
     free(): void;
 }