Add info about CUDA_VISIBLE_DEVICES (#1682)

Author: SlyEcho

README.md

@@ -310,6 +310,8 @@ Building the program with BLAS support may lead to some performance improvements
     ```
   Note: Because llama.cpp uses multiple CUDA streams for matrix multiplication results [are not guaranteed to be reproducible](https://docs.nvidia.com/cuda/cublas/index.html#results-reproducibility). If you need reproducibility, set `GGML_CUDA_MAX_STREAMS` in the file `ggml-cuda.cu` to 1.
 
+  The environment variable [`CUDA_VISIBLE_DEVICES`](https://docs.nvidia.com/cuda/cuda-c-programming-guide/index.html#env-vars) can be used to specify which GPU(s) will be used.
+
 - **CLBlast**
 
   OpenCL acceleration is provided by the matrix multiplication kernels from the [CLBlast](https://github.com/CNugteren/CLBlast) project and custom kernels for ggml that can generate tokens on the GPU.
@@ -348,7 +350,7 @@ Building the program with BLAS support may lead to some performance improvements
       cmake --install . --prefix /some/path
       ```
 
-      Where `/some/path` is where the built library will be installed (default is `/usr/loca`l`).
+      Where `/some/path` is where the built library will be installed (default is `/usr/local`).
     </details>
 
   Building: