Update README.md (Added proper build instructions with git submodule clarification)

[darkyboys]

Added this part in the README.md:

Installation

Before you install this project please make sure that you have the rocm installed. If not then please install it and check weather your gpu is supported or not.
Run this command to check the rocm support information:

rocminfo

If supported then you will be able to see it's gfx code something like gfx1100 (For RX 7900 Series), This will vary depending on the GPU Model.
If the rocm is supported then you can proceed to install ninja build system.
If everything is all right then you can proceed to run these commands:

git clone https://github.com/BillyOutlast/rocm-stable-diffusion.cpp.git
cd rocm-stable-diffusion.cpp

# Create build directory
mkdir build && cd build

# Adding ggml
git submodule update --init --recursive

# Configure CMake for ROCm (HIPBLAS)
cmake .. \
    -G Ninja \
    -DCMAKE_C_COMPILER=clang \
    -DCMAKE_CXX_COMPILER=clang++ \
    -DSD_HIPBLAS=ON \
    -DCMAKE_BUILD_TYPE=Release \
    -DAMDGPU_TARGETS=gfx1100

# Build
ninja

# Move the binary and clean the project
mv bin ../../
cd ../../
rm -rf rocm-stable-diffusion.cpp

After wards you will have the bin/sd binary file.
You can use that binary according to the documentation.

And removed the unnecessary part