add zh-cn (Simplifiled Chinese) i18n file

theme/i18n/zh-cn.json

@@ -0,0 +1,18 @@
+{
+  "LANGS_CHOOSE": "选择一种语言",
+  "GLOSSARY": "术语表",
+  "GLOSSARY_INDEX": "索引",
+  "GLOSSARY_OPEN": "术语表",
+  "GITBOOK_LINK": "本书使用 GitBook 发布",
+  "SUMMARY": "目录",
+  "SUMMARY_INTRODUCTION": "介绍",
+  "SUMMARY_TOGGLE": "目录",
+  "SEARCH_TOGGLE": "搜索",
+  "SEARCH_PLACEHOLDER": "输入并搜索",
+  "FONTSETTINGS_TOGGLE": "字体设置",
+  "SHARE_TOGGLE": "分享",
+  "SHARE_ON": "分享到 __platform__",
+  "FONTSETTINGS_WHITE": "白色",
+  "FONTSETTINGS_SEPIA": "棕褐色",
+  "FONTSETTINGS_NIGHT": "夜间"
+}