Add Link to zh-CN translation (#293)

Author: pickfire

SUMMARY.md

@@ -1,6 +1,7 @@
 # Summary
 
 - [Introduction](./intro.md)
+  - [Translations](./translations.md)
 - [Idioms](./idioms/index.md)
   - [Use borrowed types for arguments](./idioms/coercion-arguments.md)
   - [Concatenating Strings with `format!`](./idioms/concat-format.md)

translations.md

@@ -0,0 +1,6 @@
+# Translations
+
+- [简体中文](https://fomalhauthmj.github.io/patterns/)
+
+If you want to add a translation, please open an issue in the
+[main repository](https://github.com/rust-unofficial/patterns).