README.md: fixing typo as pointed out by @syoyo

README.md

@@ -22,7 +22,7 @@ Distributed and FP16 support relies on work by Christian Sarofeen and NVIDIA's
 4. Update .wav paths: `sed -i -- 's,DUMMY,ljs_dataset_folder/wavs,g' filelists/*.txt`
 5. Install [pytorch 0.4](https://github.com/pytorch/pytorch)
 6. Install python requirements or build docker image 
-    - Install python requirements: `pip install requirements.txt`
+    - Install python requirements: `pip install -r requirements.txt`
     - **OR**
     - Build docker image: `docker build --tag tacotron2 .`