Translate README.md to Traditional Chinese (#12701)

* Add README_zh-tw.md

* Add links to each README.

* Fix a mismatched term.

* Minor improvements.

* Rename language code to be more inclusive.

* Polish terms to make them fluent.

* Remove redundant spaces.

* Fix typo.

README.md

@@ -39,7 +39,11 @@ limitations under the License.
 </p>
 
 <h4 align="center">
-    <p><b>English</b> | <a href="https://github.com/huggingface/transformers/blob/master/README_zh-hans.md">简体中文</a><p>
+    <p>
+        <b>English</b> |
+        <a href="https://github.com/huggingface/transformers/blob/master/README_zh-hans.md">简体中文</a> |
+        <a href="https://github.com/huggingface/transformers/blob/master/README_zh-hant.md">繁體中文</a>
+    <p>
 </h4>
 
 <h3 align="center">

README_zh-hans.md

@@ -64,7 +64,11 @@ checkpoint: 检查点
 </p>
 
 <h4 align="center">
-    <p><a href="https://github.com/huggingface/transformers/">English</a> | <b>简体中文</b><p>
+    <p>
+        <a href="https://github.com/huggingface/transformers/">English</a> |
+        <b>简体中文</b> |
+        <a href="https://github.com/huggingface/transformers/blob/master/README_zh-hant.md">繁體中文</a>
+    <p>
 </h4>
 
 <h3 align="center">