Fix link to bertabs/README.md (#9255)

examples/seq2seq/README.md

@@ -18,7 +18,7 @@ limitations under the License.
 
 This directory contains examples for finetuning and evaluating transformers on summarization and translation tasks.
 Please tag @patil-suraj with any issues/unexpected behaviors, or send a PR!
-For deprecated `bertabs` instructions, see [`bertabs/README.md`](bertabs/README.md).
+For deprecated `bertabs` instructions, see [`bertabs/README.md`](https://github.com/huggingface/transformers/blob/master/examples/research_projects/bertabs/README.md).
 
 ### Supported Architectures