add build notes for nvidia in linux

README.md

@@ -57,12 +57,11 @@ Check dependencies: libboost-dev, libboost-system-dev, openssl.
 Download this source code, then cd to source folder. In GpuMiner folder run command $make all, it will generate xdag-gpu.  
 
 note: for nvidia graphic card. may need more 2 steps:
+
     1) copy opencl header file to project. For example 
-### Copy header file to project
         sudo cp -r /usr/local/cuda-10.0/targets/x86_64-linux/include/CL  ~/GpuMiner/CL
 
     2) install cuda-toolkit
-### Install cuda toolkit
         sudo apt-get install nvidia-cuda-toolkit
 
 ### Launch parameters: