Bug fixes and improvements (#1318)

* Sync zh and zh-hant versions

* Update en/README.md

* Add a Q&A for chapter of introduction

* Update the callout headers

* Sync zh ang zh-hant versions

* Bug fixes

zh-hant/codes/javascript/chapter_graph/graph_bfs.js

@@ -12,7 +12,7 @@ const { Vertex } = require('../modules/Vertex');
 function graphBFS(graph, startVet) {
     // 頂點走訪序列
     const res = [];
-    // 雜湊表，用於記錄已被訪問過的頂點
+    // 雜湊集合，用於記錄已被訪問過的頂點
     const visited = new Set();
     visited.add(startVet);
     // 佇列用於實現 BFS