readme : highlight OpenBLAS support (#956)

* highlight openblas support

* Update README.md

README.md

@@ -21,6 +21,7 @@ High-performance inference of [OpenAI's Whisper](https://github.com/openai/whisp
 - Runs on the CPU
 - [Partial GPU support for NVIDIA via cuBLAS](https://github.com/ggerganov/whisper.cpp#nvidia-gpu-support-via-cublas)
 - [Partial OpenCL GPU support via CLBlast](https://github.com/ggerganov/whisper.cpp#opencl-gpu-support-via-clblast)
+- [BLAS CPU support via OpenBLAS]((https://github.com/ggerganov/whisper.cpp#blas-cpu-support-via-openblas)
 - [C-style API](https://github.com/ggerganov/whisper.cpp/blob/master/whisper.h)
 
 Supported platforms:
@@ -346,6 +347,18 @@ cp bin/* ../
 
 Run all the examples as usual.
 
+## BLAS CPU support via OpenBLAS
+
+Encoder processing can be accelerated on the CPU via OpenBLAS.
+First, make sure you have installed `openblas`: https://www.openblas.net/
+
+Now build `whisper.cpp` with OpenBLAS support:
+
+```
+make clean
+WHISPER_OPENBLAS=1 make -j
+```
+
 ## Limitations
 
 - Inference only